NFS/pNFS: Report EINVAL errors from connect() to the server

With IPv6, connect() can occasionally return EINVAL if a route is
unavailable. If this happens during I/O to a data server, we want to
report it using LAYOUTERROR as an inability to connect.

Fixes: dd52128a ("NFSv4.1/pnfs Ensure flexfiles reports all connection related errors")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>