Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1136088
Description of problem:

subnet mask can be set to any IP address like (255.1.2.3)

valid masks are only 128.0.0.0, 192..., 224..., etc.

Version-Release number of selected component (if applicable):
Satellite-6.0.4-RHEL-6-20140829.0 [Sat6-GA-Snap7-Compose3]

How reproducible:
always

Steps to Reproduce:
1. # hammer subnet create --name subnet_1 --network 140.20.1.0 --mask 255.1.2.3
Subnet created