Update igb0 interface netmask on FreeBSD servers
Summary: Canonical IPs use /24, aliases /32 netmask.
Test Plan: Configuration per Ysul and WindRiver live config
Reviewers: DorianWinty, dereckson
Reviewed By: DorianWinty, dereckson
Differential Revision: https://devcentral.nasqueron.org/D2703