libbpf: Fix memleak in libbpf_netlink_recv()

Ensure that libbpf_netlink_recv() frees dynamically allocated buffer in
all code paths.

Fixes: 9c3de61 ("libbpf: Use dynamically allocated buffer when receiving netlink messages")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20220217073958.276959-1-andrii@kernel.org

tools/lib/bpf/netlink.c

@@ -176,7 +176,8 @@ static int libbpf_netlink_recv(int sock, __u32 nl_pid, int seq,
 				libbpf_nla_dump_errormsg(nh);
 				goto done;
 			case NLMSG_DONE:
-				return 0;
+				ret = 0;
+				goto done;
 			default:
 				break;
 			}
@@ -188,9 +189,10 @@ static int libbpf_netlink_recv(int sock, __u32 nl_pid, int seq,
 				case NL_NEXT:
 					goto start;
 				case NL_DONE:
-					return 0;
+					ret = 0;
+					goto done;
 				default:
-					return ret;
+					goto done;
 				}
 			}
 		}