LU-10391 lnet: add iface index to struct lnet_inetdev

LU-10391 lnet: add iface index to struct lnet_inetdev

When getting list of interfaces, get the index as well, as this can be
useful and avoid search the list of interfaces again to find it.

Test-Parameters: trivial testlist=sanity-lnet
Test-Parameters: serverversion=2.12 serverdistro=el7.9 testlist=runtests
Test-Parameters: clientversion=2.12 testlist=runtests
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I9b3b2516fd4ec1b83e2ec31e1318326ed22cb31b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48569
Reviewed-by: jsimmons <jsimmons@infradead.org>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>