LU-17666: configure lnet before add net in sanity-sec:31

LU-17666: configure lnet before add net in sanity-sec:31

If "options lnet config_on_load=1" is not configured in
modprobe.d, the lnet will not be configured when trying to
add a network. The command will hit problem.

/usr/sbin/lnetctl net add --if eth1 --net tcp999
add:
    - net:
          errno: -22
          descr: "cannot add network: Invalid argument"

Test-Parameters: trivial testlist=sanity-sec env=ONLY=31

Lustre-change: https://review.whamcloud.com/54543
Lustre-commit: e163883f76dac45a516b7d89671513d31063b7d6

Change-Id: If65b7cb372d4f04a10ea066d62f3ae43029fcf65
Signed-off-by: Li Xi <lixi@ddn.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54654
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>