RFC2131 requires that a client must choose XIDs in order to minimize
the chance of collision with another client. Selection of a random
XID at boot is a valid approach. Adjust the XID representation from
array of bytes to the more convenient uint32_t representation,
initialize the XID to a random number and increment for each request.
Refactor the dhcp test case to generate response messages with the XID
from the received message.
Change-Id: I93f180e6aa02430f807e0a97186577dc956fb653
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>
f903cb3763