libbpf: enforce strict libbpf 1.0 behaviors

Remove support for legacy features and behaviors that previously had to
be disabled by calling libbpf_set_strict_mode():
  - legacy BPF map definitions are not supported now;
  - RLIMIT_MEMLOCK auto-setting, if necessary, is always on (but see
    libbpf_set_memlock_rlim());
  - program name is used for program pinning (instead of section name);
  - cleaned up error returning logic;
  - entry BPF programs should have SEC() always.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220627211527.2245459-15-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

src/bpf.c

@@ -147,10 +147,6 @@ int bump_rlimit_memlock(void)
 {
 	struct rlimit rlim;
 
-	/* this the default in libbpf 1.0, but for now user has to opt-in explicitly */
-	if (!(libbpf_mode & LIBBPF_STRICT_AUTO_RLIMIT_MEMLOCK))
-		return 0;
-
 	/* if kernel supports memcg-based accounting, skip bumping RLIMIT_MEMLOCK */
 	if (memlock_bumped || kernel_supports(NULL, FEAT_MEMCG_ACCOUNT))
 		return 0;