socket: Skip ifa's without ifa->ifa_addr

Apparently getifaddrs() returns ifa's without an ifa_addr set.
diff --git a/src/socket.c b/src/socket.c
index 66907c8..901b8cd 100644
--- a/src/socket.c
+++ b/src/socket.c
@@ -169,6 +169,8 @@
 	}
 
 	for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
+		if (!ifa->ifa_addr)
+			continue;
 		if (sockaddr_equal(ifa->ifa_addr, addr, addrlen))
 			return 1;
 	}