casperd default listen qlen

[Kurt Lidl]

Greetings all.

A couple of months ago, we ran across a problem where the default
socket listen queue length in casperd was causing issues with
an application.

I increased the qlen to 16, which addressed the immediate problem,
and implemented a command line switch that allows the user to set
the length.

The problem report and patch are here:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202147

Could someone please review the patch?  I would like to see
this get committed so everyone can benefit from the change.

Thanks.

-Kurt