LU-13895 lnet: Prevent discovery on peer marked deletion

If a peer has been marked for deletion then we needn't perform any
other discovery operation on it. Integrate this peer state into the
top level of the discovery state machine so that it is checked before
any other state.

HPE-bug-id: LUS-9192
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: Ie9de5b0d38d720f4f49d7e4a0673a6b52f9d3d80
Reviewed-on: https://review.whamcloud.com/39604
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>