[ipv4] Accept unicast packets for the local network broadcast address

The ISC Kea DHCP server transmits its DHCPOFFER as a unicast packet
with a broadcast IPv4 destination address (255.255.255.255).  This
combination is currently rejected by iPXE.

Fix by explicitly accepting the local network broadcast address
(255.255.255.255) as a valid unicast destination address.

Reported-by: Roy Ledochowski <roy.ledochowski@hpe.com>
Tested-by: Roy Ledochowski <roy.ledochowski@hpe.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/ipv4.c

 
 	/* Discard unicast packets not destined for us */
 	if ( ( ! ( flags & LL_MULTICAST ) ) &&
+	     ( iphdr->dest.s_addr != INADDR_BROADCAST ) &&
 	     ipv4_has_any_addr ( netdev ) &&
 	     ( ! ipv4_has_addr ( netdev, iphdr->dest ) ) ) {
 		DBGC ( iphdr->src, "IPv4 discarding non-local unicast packet "