Bind outgoing sockets again.

Commit cff5a84 removed the feature of binding outgoing TCP sockets to a local
address. We now call bind() again, but only if there is exactly one listening
socket with the same address family as the destination address of the outgoing
socket.

src/net_socket.c

@@ -113,6 +113,34 @@ static bool bind_to_interface(int sd) {
 	return true;
 }
 
+static bool bind_to_address(connection_t *c) {
+	int s = -1;
+
+	for(int i = 0; i < listen_sockets; i++) {
+		if(listen_socket[i].sa.sa.sa_family != c->address.sa.sa_family)
+			continue;
+		if(s >= 0)
+			return false;
+		s = i;
+	}
+
+	if(s < 0)
+		return false;
+
+	sockaddr_t sa = listen_socket[s].sa;
+	if(sa.sa.sa_family == AF_INET)
+		sa.in.sin_port = 0;
+	else if(sa.sa.sa_family == AF_INET6)
+		sa.in6.sin6_port = 0;
+
+	if(bind(c->socket, &sa.sa, SALEN(sa.sa))) {
+		logger(DEBUG_CONNECTIONS, LOG_WARNING, "Can't bind outgoing socket: %s", strerror(errno));
+		return false;
+	}
+
+	return true;
+}
+
 int setup_listen_socket(const sockaddr_t *sa) {
 	int nfd;
 	char *addrstr;
@@ -481,6 +509,7 @@ begin:
 #endif
 
 		bind_to_interface(c->socket);
+		bind_to_address(c);
 	}
 
 	/* Connect */