LU-10391 lnet: document the accept= parameter properly

LU-10391 lnet: document the accept= parameter properly

The lnet "accept=" module parameter was incorrectly documented
as "acceptor" in the manual, even though that has never existed.

Add a subsection for the "accept" parameter, as well as the
"ip2nets" parameter to make the formatting more consistent with
the rest of this section.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I3a8d7d862172a3ced899aafbc0cff38ae73ebbe5
Reviewed-on: https://review.whamcloud.com/37699
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Aurelien Degremont <degremoa@amazon.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Joseph Gmitter <jgmitter@whamcloud.com>