staging: rtl8188eu: remove header file ethernet.h

"ethernet.h" is included in three files but only "rtw_recv.c" using two macros
defined in "ethernet.h", so move used macros in "rtw_recv.c" and
remove "include/ethernet.h" header file and inclusion of this header file.

v2:
First version of this patch failed to apply.

Signed-off-by: navin patidar <navin.patidar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>