LU-13734 lnet: Allow duplicate nets in ip2nets syntax

LU-13734 lnet: Allow duplicate nets in ip2nets syntax

Before the MR feature was implemented, it was not possible to
configure multiple interfaces on the same LNet, so the ip2nets
syntax did not allow for this. Now that we have MR feature, we should
allow it to be configured via ip2nets syntax. e.g.

o2ib(ib0) 10.10.10.1
o2ib(ib1) 10.10.10.2

A test is added for configuring LNet with kernel ip2nets parameter.

setup_netns() refactored to facilitate the new test.

cleanup_lnet() is modified to check whether lnet module is loaded
before attempting lnetctl lnet unconfigured otherwise sanity-lnet.sh
could exit with rc 234 on cleanup.

Test-Parameters: trivial testlist=sanity-lnet
HPE-bug-id: LUS-9046
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: Iafc3882035269073fd7e4abb53d138d9267f6e21
Reviewed-on: https://review.whamcloud.com/39227
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>