LU-10391 lnet: handle discovery with Netlink

LU-10391 lnet: handle discovery with Netlink

Move the LNet discover feature to the Netlink API. This change
enables the detection of remote LNet setups using large NID
addresses. We treat LNet discover as a ping doit function since
the output is nearly identical to pings. Returned are successes
as well as failed attempts to discover the requested NIDs.

Test-Parameters: trivial testlist=sanity-lnet
Change-Id: Id0eb4adcb4561cfae96040086aae85d6ff804259
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50253
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>