dlopen: take log_level argument and log in fallback stubs

Every dlopen_xxx() helper now takes an int log_level argument. It is
passed through to dlopen_many_sym_or_warn() (which in turn propagates it
to dlopen_verbose() for the library-not-installed case), and is used by
the fallback stub when support for the library is not compiled in to
emit a "<lib> support is not compiled in." message at the caller's level.
Callers pass LOG_DEBUG when gracefully degrading, or a higher level when
the failure should surface, and no longer need to log redundantly at the
call site.

As part of this, dlopen_bpf_full() (which already took a log_level) is
merged into dlopen_bpf() rather than keeping both.

The static inline fallbacks used to live in the headers, which required
pulling log.h in from every header that declared a dlopen_xxx(). Move
them into the .c files instead: the declaration is always outside the
#if HAVE_XXX block, the impl sits outside the outer #if HAVE_XXX wrap
with its own internal #if HAVE_XXX/#else/#endif, and apparmor-util.c,
idn-util.c, libmount-util.c and pam-util.c are now always compiled so
they can host their stubs.

src/udev/test-udev-rule-runner.c

@@ -103,7 +103,7 @@ static int run(int argc, char *argv[]) {
 
         /* Let's make sure the test runs with selinux assumed disabled. */
 #if HAVE_SELINUX
-        if (dlopen_libselinux() >= 0)
+        if (dlopen_libselinux(LOG_DEBUG) >= 0)
                 sym_fini_selinuxmnt();
 #endif
         mac_selinux_retest();

src/udev/udev-builtin-blkid.c

@@ -513,7 +513,7 @@ static int builtin_blkid(UdevEvent *event, int argc, char *argv[]) {
                 {}
         };
 
-        r = dlopen_libblkid();
+        r = dlopen_libblkid(LOG_DEBUG);
         if (r < 0)
                 return log_device_debug_errno(dev, r, "blkid not available: %m");
 

src/udev/udevd.c

@@ -58,11 +58,11 @@ int run_udevd(int argc, char *argv[]) {
                 return log_error_errno(r, "Failed to create /run/udev: %m");
 
         /* Load some shared libraries before we fork any workers */
-        (void) dlopen_libacl();
-        (void) dlopen_libblkid();
-        (void) dlopen_libkmod();
-        (void) dlopen_libmount();
-        (void) dlopen_tpm2();
+        (void) dlopen_libacl(LOG_DEBUG);
+        (void) dlopen_libblkid(LOG_DEBUG);
+        (void) dlopen_libkmod(LOG_DEBUG);
+        (void) dlopen_libmount(LOG_DEBUG);
+        (void) dlopen_tpm2(LOG_DEBUG);
 
         if (arg_daemonize) {
                 pid_t pid;