Initial import of p5-Net-SNMP-Mixin version 0.12 in the NetBSD

Initial import of p5-Net-SNMP-Mixin version 0.12 in the NetBSD
Packages Collection.

The Perl 5 module Net::SNMP::Mixin is a thin framework to access
cooked SNMP information from SNMP agents with various mixins to
Net::SNMP. This module provides helper functions in order to mixin
methods into the inheritance tree of the Net::SNMP session instances
or the Net::SNMP class itself