Make dhclient use bootpc (68) as the source port for unicast
DHCPREQUEST packets instead of allowing the protocol stack to pick
a random source port.
This fixes the behaviour where dhclient would never transition
from RENEWING to BOUND without going through REBINDING in networks
which are paranoid about DHCP spoofing, such as most mainstream
cable-broadband ISP networks.
Obtained from: OpenBSD
Reviewed by: brooks
Approved by: re (kib)