NFSv4.1 remove xprt from xprt_switch if session trunking test fails

If we are doing a session trunking test and it fails for the transport,
then remove this transport from the xprt_switch group.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>