LU-12815 socklnd: allow dynamic setting of conns_per_peer

LU-12815 socklnd: allow dynamic setting of conns_per_peer

Modify lnetctl and associated code to allow dynamic setting
of conns_per_peer lnd parameter per ni.

The parameter can be set for a specific active nid:
        lnetctl net set --nid 192.168.122.10@tcp --conns-per-peer=4

Or when adding a new net, taking effect on the new nid:
        lnetctl net add --net tcp --if eth0 --conns-per-peer=1

By default, conns_per_peer value specified as the module parameter
shall be used.

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I11625b9ad61f0311c294001a38b7855465491aaf
Reviewed-on: https://review.whamcloud.com/41463
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>