802.3

Hey,

I needed to filter 802.3 packets based on the their SSAP/DSAP values and SNAP type.

Wrote an extension I'd like to share.  Basically I just ripped off the ARP kernel/userspace stuff.

Adds:  

--802.3-sap 
--802.3-type

sap's argument is a one byte hex value.  type takes a two byte hex value.  -p must be LENGTH.  The
file _ebt_802.c is the userspace file.

--802.3-type will only check 802.3 packets with sap value 0xaa (which is the correct behavior).  

Comments are welcome.  If you guys think it looks alright I'll add 802.3 control matching later this week.

Enjoy!

vitale