Added source-port-range-{min,max} to sec. groups

Added source-port-range-{min,max} to security groups frontend API and DB. The
attributes are already in the RPC API and are compatible with existing
implementations.

Partially-implements: blueprint ovs-firewall-driver

DocImpact: Adding these parameters to the API via extension requires
documentation changes.

Change-Id: I8cb4f77d847f79dfde7d5cf4a789c19af5c3bc4a