Add missing quota flags in the config file sample

l3 extensions don't set quota flags in the config sample file
etc/neutron.conf.
Quota is unlimited if its value is minus and not only if it's -1.

Closes-Bug: #1250574
Change-Id: I76c8d1e2676d4e9b0feeed6e504e759fe736a0db
Merge "Add missing quota flags in the config file sample"