tree-wide: drop MSG_NOSIGNAL flag from recvmsg() invocations

MSG_NOSIGNAL is only defined for sendmsg(), not for recvmsg(), hence
let's drop it's use, in particular as it appears to create problems on
older kernels. See:

https://lists.freedesktop.org/archives/systemd-devel/2018-June/040869.html

src/portable/portable.c

@@ -201,7 +201,7 @@ static int recv_item(
         assert(ret_name);
         assert(ret_fd);
 
-        n = recvmsg(socket_fd, &mh, MSG_NOSIGNAL|MSG_CMSG_CLOEXEC);
+        n = recvmsg(socket_fd, &mh, MSG_CMSG_CLOEXEC);
         if (n < 0)
                 return -errno;