This patch adds support for virtual LAN (VLAN) tagging. VLAN tagging allows
multiple VLANs in a bridged network to share the same physical network link
but maintain isolation:
http://en.wikipedia.org/wiki/IEEE_802.1Q
* grub-core/net/ethernet.c: Add check, get, and set vlan tag id.
* grub-core/net/drivers/ieee1275/ofnet.c: Get vlan tag id from bootargs.
* grub-core/net/arp.c: Add check.
* grub-core/net/ip.c: Likewise.
* include/grub/net/arp.h: Add vlantag attribute.
* include/grub/net/ip.h: Likewise.
* include/grub/net/arp.h: added arp header, arp cache entry and related constants and functions
* net/arp.c: added functions arp_init_table, arp_find_entry, arp_resolve and arp_receive
* net/ethernet.c (send_ethernet_packet): replaced hardcoded hardware address by parameter target_addr
* net/ethernet.c (recv_ethernet_packet): added call to arp_receive when packet is of type 0x803 (ARP) and only return when packet is of type determined by parameter ethertype
* net/ip.c (send_ip_packet): added call to arp_resolve to determine hardware address of destination
* net/netbuff.c (grub_netbuff_alloc): fixed swapped parameters in call to grub_memalign
