SUNRPC: Fix a hang in TLS sock_close if sk_write_pending

SUNRPC: Fix a hang in TLS sock_close if sk_write_pending

We've observed an NFS server shrink the TCP window and then reset the TCP
connection as part of a HA failover.  When the connection has TLS, often
the NFS client will hang indefinitely in this stack:

     wait_woken+0x70/0x80
     wait_on_pending_writer+0xe4/0x110 [tls]
     tls_sk_proto_close+0x368/0x3a0 [tls]
     inet_release+0x54/0xb0
     __sock_release+0x48/0xc8
     sock_close+0x20/0x38
     __fput+0xe0/0x2f0
     __fput_sync+0x58/0x70
     xs_reset_transport+0xe8/0x1f8 [sunrpc]
     xs_tcp_shutdown+0xa4/0x190 [sunrpc]
     xprt_autoclose+0x68/0x170 [sunrpc]
     process_one_work+0x180/0x420
     worker_thread+0x258/0x368
     kthread+0x104/0x118
     ret_from_fork+0x10/0x20

This hang prevents the client from closing the socket and reconnecting to
the server.

Because xs_nospace() elevates sk_write_pending, and sk_sndtimeo is
MAX_SCHEDULE_TIMEOUT, tls_sk_proto_close is never able to complete its wait
for pending writes to the socket.  For this case where we are resetting the
transport anyway, we don't expect the socket to ever have write space, so
fix this by simply clearing the sock's sndtimeo under the sock's lock.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>