SUNRPC: Ensure that the TCP socket is closed when in CLOSE_WAIT

commit a519fc7a70d1a918574bb826cc6905b87b482eb9 upstream.

Instead of doing a shutdown() call, we need to do an actual close().
Ditto if/when the server is sending us junk RPC headers.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Tested-by: Simon Kirby <sim@hostway.ca>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>