"linux-includes/netinet/if_ether.h" to "ethertype.h".
Move other stuff used by dissectors from <netinet/if_ether.h> to
"ether.h", along the lines of "fddi.h" and "token.h".
Move ARP declarations from BSD include files to "print-arp.c".
Remove from dissectors includes of <netinet/if_ether.h>, and add
includes of "ethertype.h" and/or "ether.h" as necessary.
Get rid of configuration options that test declarations now made in
"ether.h" or "print-arp.c", as those declarations are now under our
control, not the OS's control.
