odhcpd: remove mac_len argument to ubus_bcast_dhcp_event()

odhcpd: remove mac_len argument to ubus_bcast_dhcp_event()

All the places that call ubus_bcast_dhcp_event() have already checked that the
hardware adress is a MAC address, and it's not like we support anything else,
so remove the length argument.

The function is actually DHCPv4 specific, but that's a topic for another time.

Signed-off-by: David Härdeman <[email protected]>
Link: https://github.com/openwrt/odhcpd/pull/270
Signed-off-by: Álvaro Fernández Rojas <[email protected]>