bpf: various coding style fixes

Mostly logging related: let's downgrade logging in dlopen_bpf() for
example, and remove duplicate logging at various places. Add %m to log
messages and so on.

src/shared/bpf-dlopen.c

@@ -37,7 +37,7 @@ int dlopen_bpf(void) {
 
         r = dlsym_many_and_warn(
                         dl,
-                        LOG_ERR,
+                        LOG_DEBUG,
                         DLSYM_ARG(bpf_link__destroy),
                         DLSYM_ARG(bpf_link__fd),
                         DLSYM_ARG(bpf_map__fd),
@@ -60,7 +60,6 @@ int dlopen_bpf(void) {
         /* Note that we never release the reference here, because there's no real reason to, after all this
          * was traditionally a regular shared library dependency which lives forever too. */
         bpf_dl = TAKE_PTR(dl);
-
         return 1;
 }
 

src/shared/bpf-link.c

@@ -6,15 +6,11 @@
 
 bool can_link_bpf_program(struct bpf_program *prog) {
         _cleanup_(bpf_link_freep) struct bpf_link *link = NULL;
-        int r;
 
         assert(prog);
 
-        r = dlopen_bpf();
-        if (r < 0) {
-                log_debug_errno(r, "Could not load libbpf: %m");
+        if (dlopen_bpf() < 0)
                 return false;
-        }
 
         /* Pass invalid cgroup fd intentionally. */
         link = sym_bpf_program__attach_cgroup(prog, /*cgroup_fd=*/-1);
@@ -24,8 +20,6 @@ bool can_link_bpf_program(struct bpf_program *prog) {
 }
 
 int serialize_bpf_link(FILE *f, FDSet *fds, const char *key, struct bpf_link *link) {
-        int fd;
-
         assert(key);
 
         if (!link)
@@ -34,11 +28,11 @@ int serialize_bpf_link(FILE *f, FDSet *fds, const char *key, struct bpf_link *li
         if (sym_libbpf_get_error(link) != 0)
                 return -EINVAL;
 
-        fd = sym_bpf_link__fd(link);
-        return serialize_fd(f, fds, key, fd);
+        return serialize_fd(f, fds, key, sym_bpf_link__fd(link));
 }
 
 struct bpf_link *bpf_link_free(struct bpf_link *link) {
+
         /* Avoid a useless dlopen() if link == NULL */
         if (!link)
                 return NULL;