LU-9121 lnet: foundation patch for selection mod

LU-9121 lnet: foundation patch for selection mod

Add the priority and preferred NIDs fields in the lnet_ni,
lnet_net, lnet_peer_net and lnet_peer_ni. Switched
the implementation of the preferred NIDs list to list_head
instead of array, because the code is more straight forward.
There is more memory overhead due to list_head, but these lists
are expected to be small, so I chose code simplicity over memory.

Test-Parameters: trivial testlist=lnet-selftest,sanity-lnet
Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I0c75855b736345c25e1604083eee2b65d38ef28d
Reviewed-on: https://review.whamcloud.com/34350
Reviewed-by: Chris Horn <chris.horn@hpe.com>