LU-18637 obd: add 'network' server mount option

LU-18637 obd: add 'network' server mount option

Just like the '-o network' client option, we want to control which
LNet network is used for connections established by servers to remote
peers (MGS, other servers).
This controls the following connections:
- osp
- lwp
- mgc
This patch leverages the 'imp_conn_restricted_net' field on the
'struct obd_import'.

Enhance sanity-sec test_31 to exercise this '-o network' option on
server side.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I39cbab2645aeda6fe54efb377d1b1d9edfceb89f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57780
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>