In contrast to BOOTP, DHCP uses a 4-way handshake, so requires to send
packets more often.
Refactor the generation and sending of the BOOTREQUEST packet into
a separate function, so that future code can more easily reuse this.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>