Fix our *ether* headers mess.

Move everything to where it should be.

Along the way, we lose <net/ethertypes.h>. glibc only has a handful of these
types, and they're all in <net/ethernet.h>, not <net/ethertypes.h>. I've taken
the liberty of not including the AppleTalk ones, since it is 2016.

Also, <net/if_ether.h> should be <netinet/if_ether.h> (though with different
contents).

Bug: http://b/28519060
Change-Id: Ia41c3fc136fd3e6b008c8d08018e0629134ea6fc