Description of problem:
Setting Prefix on a network instead of netmask recognized as a difference and network considered as unsynced.

As part of the [RFE] Allow filling also network prefix to 'netmask' fields of static IP configuration - BZ  1012881 that is already verified by me and worked fine, it is now allowed to fill Prefix (0-32) in the netmask field. But now, setting Prefix causing the network to be unsynced. 
- If using netmask(255.255.255.0 for example) network is synced.
- If using Prefix (24 or /24 for example) network becomes unsynced once approving operation via Setup Networks.

Version-Release number of selected component (if applicable):
3.6.0-0.18.el6
vdsm-4.17.8-1.el7ev.noarch

How reproducible:
100

Steps to Reproduce:
1. Create new network and attach to host
2. Edit network(pencil) and set static ip 7.7.7.7 with Routing Prefix 24 or /24
3. Approve operation

Actual results:
Network become unsynced. A difference is recognized for some reason. 
The 'out-of-sync' tool tip displays:
Host network's configurations differ from DC
Host - 255.255.255.0
DC /24

Expected results:
Network should be synced.
Used to work fine on 3.6.0-0.0.master.20150412172306.git55ba764.el6
with vdsm-4.17.0-632.git19a83a2.el7.x86_64. 


Additional info:
See also https://bugzilla.redhat.com/show_bug.cgi?id=1012881