LU-17230 socklnd: treat UNKNOWN netif operstate as UP

LU-17230 socklnd: treat UNKNOWN netif operstate as UP

"UNKNOWN" (IF_OPER_UNKNOWN) operational state doesn't necessarily
mean that the interface can't be used and may be the result of
particular network driver not providing UP/DOWN states,
so it may be incorrect for socklnd to initiate
setting of a "fatal error" flag on a NI using an interface
in "UNKNOWN" operstate.

Lustre-change: https://review.whamcloud.com/52842
Lustre-commit: 6897dbe67c0d7d7554926128a17c65afa1ec0001

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I39dfa01f3758809440d50cf8b6b11555889ef366
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53285
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>