l3_agent: make process_router more robust

If internal_network_added/removed fails, _sync_routers_task will call
process_router to do fault recovery. Because the port is already
added/removed to/from ri.internal_ports, internal_network_added or
internal_network_removed will not be called again.

The patch fix this issue by calling ri.internal_ports.append/removed
only if internal_network_added/removed succeed. Without the patch,
the added testcases would fail.

Change-Id: I2d2e004caa670c1624257c1d7ccc900438b42d08
Co-Authored-By: Hirofumi Ichihara <ichihara.hirofumi@lab.ntt.co.jp>
Closes-Bug: #1255871
Remove dead code _arp_spoofing_rule()

This code should have been removed when the allowed_address_pair
extension was added here (0efce6195fa7be80e110bd841dc9b3537a94c376).
The arp spoofing rules are handled in the method _setup_spoof_filter_chain().

Reported by: Amir Sadoughi that this was crud I left behind :)

Change-Id: Ib0e2e2a5c13fb8fa7af1f988510143f40ac335e2
Closes-bug: #1258629
Merge "Remove dead code _arp_spoofing_rule()"
Merge "l3_agent: make process_router more robust"