net: dsa: reduce number of protocol hooks

DSA is currently registering one packet_type function per EtherType it needs to intercept in the receive path of a DSA-enabled Ethernet device. Right now we have three of them: trailer, DSA and eDSA, and there might be more in the future, this will not scale to the addition of new protocols. This patch proceeds with adding a new layer of abstraction and two new functions: dsa_switch_rcv() which will dispatch into the tag-protocol specific receive function implemented by net/dsa/tag_*.c dsa_slave_xmit() which will dispatch into the tag-protocol specific transmit function implemented by net/dsa/tag_*.c When we do create the per-port slave network devices, we iterate over the switch protocol to assign the DSA-specific receive and transmit operations. A new fake ethertype value is used: ETH_P_XDSA to illustrate the fact that this is no longer going to look like ETH_P_DSA or ETH_P_TRAILER like it used to be. This allows us to greatly simplify the check in eth_type_trans() and always override the skb->protocol with ETH_P_XDSA for Ethernet switches tagged protocol, while also reducing the number repetitive slave netdevice_ops assignments.

FFFlorian Fainelli committed 12 years ago