Revert "Style network address for subnet as required field"

This reverts commit 9f9b197fa077dabf5884242507f52528b99f1918.

The reverted commit completely breaks IPv6 network creation
workflow. In the network creation workflow, when IPv6 is selected
in "IP version", all subnet related fields will be hidden and
users cannot created a network with IPv6 subnet.

Change-Id: I6c974ac4c890543166117253400cb6c827aa0fb8
Closes-Bug: #1371901
Related-Bug: #1367858
Merge "Revert "Style network address for subnet as required field""