LU-13641 socklnd: replace route construct

LU-13641 socklnd: replace route construct

With TCP bonding removed, it's no longer necessary to
maintain multiple route constructs per peer_ni in socklnd.
Replace the route construct with connection control block,
conn_cb, and make sure there's a single conn_cb per peer_ni.

Lustre-change: https://review.whamcloud.com/40774
Lustre-commit: 7766f01e891c378d1bf099e475f128ea612488f0

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I1de683429af5f93b3197b6d536e80b5ac1e67a22
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/44327
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>