SetSelfIP unconditionally accessed t.dhcp, but t.dhcp is only
initialized when DHCP discovery is enabled. A network change event
can fire SetSelfIP regardless of the discovery configuration,
causing a nil pointer dereference.
Guard the t.dhcp access with a nil check so the self IP is still
updated on the Table even when DHCP discovery is disabled.
An interface may have multiple MAC addresses, that leads to the problem
when looking up hostname for its multiple <ip, mac> pairs, because the
"ip" map, which storing "mac => ip" mapping can only store 1 entry. It
ends up returns an empty hostname for a known MAC address.
Fixing this by filling empty hostname based on clients which is already
listed, ensuring all clients with the same MAC address will have the
same hostname information.
Cuong Manh Le