DHCP regression on 2009-06

Fixed the DHCP/BOOTP/RARP regression introduced in u-boot-2009.06
by initializing our IP addr to 0 in order to accept any IP addr
assigned to us by the DHCP/BOOTP/RARP server.

Ack-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>