LU-13929 lnet: modify assertion in lnet_post_send_locked

LU-13929 lnet: modify assertion in lnet_post_send_locked

Check that the pointer to the local interface is not NULL
before asserting. While checking if local ni is the destination,
the assertion may attempt to dereference pointer to local
interface after it has already been cleaned up on shutdown.

Lustre-change: https://review.whamcloud.com/40749
Lustre-commit: e5a8f3fc12840aee97fca03d76b1ae9b4572acb8

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I0f4be04a728a7243823bec70f9efbe52bcb104b3
Reviewed-on: https://review.whamcloud.com/48265
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>