Increase size of peer_address attribute in VPNaaS

Increased the size so that peer_address could be FQDN. API
document changed constraint from IPAddress to string, however
in the plugin/service code, it is already a string and there is
no specific restriction on the value. Database migration will
be performed, due to the size change.

bug 1225128

Change-Id: Idc0d545491074fc0a1a3bd0256fdbba0a3a0718c
Merge "Increase size of peer_address attribute in VPNaaS"