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
Merge "Set default fixed_ip quota to unlimited."