Change the interface of the function dealing with incoming BOOTP packets
to take an interface instead of a card, to allow more fine per-interface
state (timeout, handshake state) later on.
Use the opportunity to clean up the code a bit.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>