SUNRPC: Handle connection reset more efficiently.

If the connection reset is due to an active call on our side, then
the state change is sometimes not reported. Catch those instances
using xs_error_report() instead.
Also remove the xs_tcp_shutdown() call in xs_tcp_send_request() as
the change in behaviour makes it redundant.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>