LU-12815 socklnd: add conns_per_peer parameter

LU-12815 socklnd: add conns_per_peer parameter

Introduce conns_per_peer ksocklnd module parameter.
In typed mode, this parameter shall control
the number of BULK_IN and BULK_OUT tcp connections,
while the number of CONTROL connections shall stay
at 1. In untyped mode, this parameter shall control
the number of untyped connections.
The default conns_per_peer is 1. Max is 127.

Lustre-change: https://review.whamcloud.com/41056
Lustre-commit: 71b2476e4ddb95aa42f4a0ea3f23b1826017bfa5

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I70bbaf7899ae1fbc41de34553c8c4ad1c7d55f7e
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/44328
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>