libkmod: turn into dlopen() dependency

As it turns out libkmod has quite a bunch of deps, including various
compressing libs and similar. By turning this into a dlopen()
dependency, we can make our depchain during install time quite a bit
smaller. In particular as inside of containers kmod doesn't help anyway
as CAP_SYS_MODULE is not available anyway.

While we are at it, also share the code that sets up logging/kmod
context.

After:

$ lddtree ./build/systemd
systemd => ./build/systemd (interpreter => /lib64/ld-linux-x86-64.so.2)
    libsystemd-core-255.so => ./build/src/core/libsystemd-core-255.so
        libaudit.so.1 => /lib64/libaudit.so.1
            libcap-ng.so.0 => /lib64/libcap-ng.so.0
                ld-linux-x86-64.so.2 => /lib64/ld-linux-x86-64.so.2
        libm.so.6 => /lib64/libm.so.6
        libmount.so.1 => /lib64/libmount.so.1
            libblkid.so.1 => /lib64/libblkid.so.1
        libseccomp.so.2 => /lib64/libseccomp.so.2
        libselinux.so.1 => /lib64/libselinux.so.1
            libpcre2-8.so.0 => /lib64/libpcre2-8.so.0
    libsystemd-shared-255.so => /home/lennart/projects/systemd/build/src/shared/libsystemd-shared-255.so
        libacl.so.1 => /lib64/libacl.so.1
            libattr.so.1 => /lib64/libattr.so.1
        libcap.so.2 => /lib64/libcap.so.2
        libcrypt.so.2 => /lib64/libcrypt.so.2
        libgcrypt.so.20 => /lib64/libgcrypt.so.20
            libgpg-error.so.0 => /lib64/libgpg-error.so.0
        liblz4.so.1 => /lib64/liblz4.so.1
        libcrypto.so.3 => /lib64/libcrypto.so.3
            libz.so.1 => /lib64/libz.so.1
        libpam.so.0 => /lib64/libpam.so.0
            libeconf.so.0 => /lib64/libeconf.so.0
        liblzma.so.5 => /lib64/liblzma.so.5
        libzstd.so.1 => /lib64/libzstd.so.1
    libc.so.6 => /lib64/libc.so.6

Before:

$ lddtree ./build/systemd
systemd => ./build/systemd (interpreter => /lib64/ld-linux-x86-64.so.2)
    libsystemd-core-255.so => ./build/src/core/libsystemd-core-255.so
        libaudit.so.1 => /lib64/libaudit.so.1
            libcap-ng.so.0 => /lib64/libcap-ng.so.0
                ld-linux-x86-64.so.2 => /lib64/ld-linux-x86-64.so.2
        libkmod.so.2 => /lib64/libkmod.so.2
            libzstd.so.1 => /lib64/libzstd.so.1
            liblzma.so.5 => /lib64/liblzma.so.5
            libz.so.1 => /lib64/libz.so.1
            libcrypto.so.3 => /lib64/libcrypto.so.3
            libgcc_s.so.1 => /lib64/libgcc_s.so.1
        libm.so.6 => /lib64/libm.so.6
        libmount.so.1 => /lib64/libmount.so.1
            libblkid.so.1 => /lib64/libblkid.so.1
        libseccomp.so.2 => /lib64/libseccomp.so.2
        libselinux.so.1 => /lib64/libselinux.so.1
            libpcre2-8.so.0 => /lib64/libpcre2-8.so.0
    libsystemd-shared-255.so => /home/lennart/projects/systemd/build/src/shared/libsystemd-shared-255.so
        libacl.so.1 => /lib64/libacl.so.1
            libattr.so.1 => /lib64/libattr.so.1
        libcap.so.2 => /lib64/libcap.so.2
        libcrypt.so.2 => /lib64/libcrypt.so.2
        libgcrypt.so.20 => /lib64/libgcrypt.so.20
            libgpg-error.so.0 => /lib64/libgpg-error.so.0
        liblz4.so.1 => /lib64/liblz4.so.1
        libpam.so.0 => /lib64/libpam.so.0
            libeconf.so.0 => /lib64/libeconf.so.0
    libc.so.6 => /lib64/libc.so.6

src/modules-load/modules-load.c

@@ -23,14 +23,6 @@ static const char conf_file_dirs[] = CONF_PATHS_NULSTR("modules-load.d");
 
 STATIC_DESTRUCTOR_REGISTER(arg_proc_cmdline_modules, strv_freep);
 
-static void systemd_kmod_log(void *data, int priority, const char *file, int line,
-                             const char *fn, const char *format, va_list args) {
-
-        DISABLE_WARNING_FORMAT_NONLITERAL;
-        log_internalv(priority, 0, file, line, fn, format, args);
-        REENABLE_WARNING;
-}
-
 static int add_modules(const char *p) {
         _cleanup_strv_free_ char **k = NULL;
 
@@ -156,7 +148,7 @@ static int parse_argv(int argc, char *argv[]) {
 }
 
 static int run(int argc, char *argv[]) {
-        _cleanup_(kmod_unrefp) struct kmod_ctx *ctx = NULL;
+        _cleanup_(sym_kmod_unrefp) struct kmod_ctx *ctx = NULL;
         int r, k;
 
         r = parse_argv(argc, argv);
@@ -171,12 +163,9 @@ static int run(int argc, char *argv[]) {
         if (r < 0)
                 log_warning_errno(r, "Failed to parse kernel command line, ignoring: %m");
 
-        ctx = kmod_new(NULL, NULL);
-        if (!ctx)
-                return log_oom();
-
-        kmod_load_resources(ctx);
-        kmod_set_log_fn(ctx, systemd_kmod_log, NULL);
+        r = module_setup_context(&ctx);
+        if (r < 0)
+                return log_error_errno(r, "Failed to initialize libkmod context: %m");
 
         r = 0;