LU-16552 test: add new lnet test for Multi-Rail setups

LU-16552 test: add new lnet test for Multi-Rail setups

You can crash lnet kernel module by setting up a interface with
lctl net up and then attempting to setup the interface with
the import function. This is due to improper clearing the net_cpts
array.

Currently sanity-lnet.sh doesn't real test MR setups. Because of
this a few bugs slipped in. Add two new test to ensure MR setups
behave properly. Test 107 is to see if deleting a second interface
for a MR setup doesn't crash a node. Test 108 creates a multi rail
setup of a tcp LNet net with two interfaces, one real and the
other fake. A bug was preventing the second fake interface from
being added.

Test-Parameters: trivial testlist=sanity-lnet
Change-Id: Ic69e14bd0617f4d6fe931140b5b6d43b795843cf
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50302
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>