libbpf: Add missing LIBBPF_API annotation to libbpf_set_memlock_rlim API

LIBBPF_API annotation seems missing on libbpf_set_memlock_rlim API, so
add it to make this API callable from libbpf's shared library version.

Fixes: e542f2c4 ("libbpf: Auto-bump RLIMIT_MEMLOCK if kernel needs it for BPF")
Fixes: ab9a5a05 ("libbpf: fix up few libbpf.map problems")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20240201172027.604869-3-andrii@kernel.org

tools/lib/bpf/bpf.h

@@ -35,7 +35,7 @@
 extern "C" {
 #endif
 
-int libbpf_set_memlock_rlim(size_t memlock_bytes);
+LIBBPF_API int libbpf_set_memlock_rlim(size_t memlock_bytes);
 
 struct bpf_map_create_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */