svcrpc: don't error out on small tcp fragment

Though clients we care about mostly don't do this, it is possible for
rpc requests to be sent in multiple fragments.  Here we have a sanity
check to ensure that the final received rpc isn't too small--except that
the number we're actually checking is the length of just the final
fragment, not of the whole rpc.  So a perfectly legal rpc that's
unluckily fragmented could cause the server to close the connection
here.

Cc: stable@vger.kernel.org
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

net/sunrpc/svcsock.c

@@ -1095,7 +1095,7 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 		goto err_noclose;
 	}
 
-	if (svc_sock_reclen(svsk) < 8) {
+	if (svsk->sk_datalen < 8) {
 		svsk->sk_datalen = 0;
 		goto err_delete; /* client is nuts. */
 	}