fd-util: move cmsg_close_all() to socket-util.[ch]

This call only makes sense on sockets, it's not a generic fd concept,
hence let's move this over.

src/basic/socket-util.c

@@ -1981,3 +1981,21 @@ int socket_get_cookie(int fd, uint64_t *ret) {
 
         return 0;
 }
+
+void cmsg_close_all(struct msghdr *mh) {
+        assert(mh);
+
+        struct cmsghdr *cmsg;
+        CMSG_FOREACH(cmsg, mh) {
+                if (cmsg->cmsg_level != SOL_SOCKET)
+                        continue;
+
+                if (cmsg->cmsg_type == SCM_RIGHTS)
+                        close_many(CMSG_TYPED_DATA(cmsg, int),
+                                   (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int));
+                else if (cmsg->cmsg_type == SCM_PIDFD) {
+                        assert(cmsg->cmsg_len == CMSG_LEN(sizeof(int)));
+                        safe_close(*CMSG_TYPED_DATA(cmsg, int));
+                }
+        }
+}