Fix handling of port-range-min 0 in secgroup RPC and agent

Fix handling of port-range-min 0 in secgroup RPC and agent

For TCP/UDP protocol, port valid range is 0 to 65535, so for a
security group rule, its valid range is also 0 to 65535. this
patch makes two changes:
1. if a security group rule port_range_min is 0, l2 agent also can
   get port_range_min real value 0 when it gets this rule for a
   device via RPC.
2. For IptablesFirewallDriver, if port range is [0, xxxx], l2 agent
   also need add this rule to iptables.

Change-Id: If93c54a31d973187889ead2c2797ffdd40a4393d
Closes-bug: #1473965