Set default fixed_ip quota to unlimited.

DocImpact: our previous default quota of ten was poorly thought through
and resulted in upgrade problems. Instead, let's have operators opt into
fixed IP quotas. This change should be mentioned in release notes please.

Resolves bug 1161190.

Change-Id: I2f066a0129461899fe330a628cf49ee5273eaba4
(cherry picked from commit 78c7edc52efdf31d844b8bb38c2460add4c864fb)
Merge "Set default fixed_ip quota to unlimited." into stable/folsom