BUG/MINOR: sockpair: wrong return value for fd_send_uxst()

The fd_send_uxst() function which is used to send a socket over the
socketpair returns 1 upon error instead of -1, which means the error
case of the sendmsg() is never catched correctly.

Must be backported as far as 1.9.

src/proto_sockpair.c

@@ -246,7 +246,7 @@ int send_fd_uxst(int fd, int send_fd)
 
 	if (sendmsg(fd, &msghdr, 0) != sizeof(iobuf)) {
 		ha_warning("Failed to transfer socket\n");
-		return 1;
+		return -1;
 	}
 
 	return 0;