ipconfig: handle case of delayed DHCP server

ipconfig: handle case of delayed DHCP server

If a DHCP server is delayed, it's possible for the client to receive the
DHCPOFFER after it has already sent out a new DHCPDISCOVER message from
a second interface.  The client then sends out a DHCPREQUEST from the
second interface, but the server doesn't recognize the device and
rejects the request.

This patch simply tracks the current device being configured and throws
away the OFFER if it is not intended for the current device.  A more
sophisticated approach would be to put the OFFER information into the
struct ic_device rather than storing it globally.

Signed-off-by: Chris Friesen <cfriesen@nortel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>