samples/bpf: make map creation more verbose

map creation is typically the first one to fail when rlimits are
too low, not enough memory, etc
Make this failure scenario more verbose
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

samples/bpf/bpf_load.c

@@ -158,8 +158,11 @@ static int load_maps(struct bpf_map_def *maps, int len)
 					   maps[i].key_size,
 					   maps[i].value_size,
 					   maps[i].max_entries);
-		if (map_fd[i] < 0)
+		if (map_fd[i] < 0) {
+			printf("failed to create a map: %d %s\n",
+			       errno, strerror(errno));
 			return 1;
+		}
 
 		if (maps[i].type == BPF_MAP_TYPE_PROG_ARRAY)
 			prog_array_fd = map_fd[i];