Ignore exception on router interface delete if router deleted
Ignore exception on router interface delete if router deleted

Ignore exception on router interface if the interface was
already deleted or the logical router doesnt exist.

Change-Id: I8b53bc9087f7593bb35d2abead7ccf8a7342a38d

FrankDuan/df_code,openstack/dragonflow,openstack/dragonflow,openstack/dragonflow,FrankDuan/df_code,FrankDuan/df_code