Merge pull request #5009 from donaldsharp/interface_deletion

lib, zebra: Allow for interface deletion when kernel event happens

diff --cc isisd/isis_circuit.h
Simple merge

diff --cc lib/if.c
Simple merge

diff --cc ospf6d/ospf6_interface.c
Simple merge

diff --cc pimd/pim_zebra.c
Simple merge

diff --cc staticd/static_zebra.c
Simple merge

diff --cc zebra/if_netlink.c
Simple merge

diff --cc zebra/interface.c
Simple merge