The net_dhcpv4_stop() function stops the event listener for any IF_UP
events previously. In case multiple interfaces are used and optionally
being switched over, it could result in disabling dhcp unintentionally.
The callback is initialized at the init function and added/removed in
the start/stop function based on the interface list being empty
or not. (first added, last removed)
The event handler checks if the interface is in the list before acting
on it.
Signed-off-by: Vincent van der Locht <vincent@vlotech.nl>
58463b7ea7