Add a routine to convert Ethernet packet types to strings.

	Add a routine to convert Ethernet packet types to strings.

	Use that routine in "ethertype()".

	Have "dissect_arp()" handle hardware addresses that aren't
	6-byte Ethernet addresses and protocol addresses that aren't
	4-byte IPv4 addresses - currently, it just prints the first 16
	hex digits, but it could be made to handle other types specially
	just as it handles 6-byte Ethernet and 4-byte IPv4 addresses.

	Have it decode a more complete set of hardware address types.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@78 f5534014-38df-0310-8fa8-9805f1628bb7