svcrpc: complete svsk processing on cb receive failure

Currently when there's some failure to receive a callback (because we
couldn't find a matching xid, for example), we exit svc_recv with
sk_tcplen still set but without any pages saved with the socket.  This
will cause a crash later in svc_tcp_restore_pages.

Instead, make sure we reset that tcp information whether the callback
received failed or succeeded.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>