rx: avoid nat ping during shutdown

rx: avoid nat ping during shutdown

shutdown_rx, unlike rx_Finalize, kills the socket before the conns.
since we call osi_NetSend directly, we lose. just do a simple
check for rxinit_status, and exit immediately before sending if rx
is not up.

Reviewed-on: http://gerrit.openafs.org/5377
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 8d939c08f60b44c83ed8db8892b93563ddea0e15)

Change-Id: Ic22dc3b6e6c6d330eeabddead7ed8f0a0da73b57
Reviewed-on: http://gerrit.openafs.org/5407
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>