staging: et131x: Converting et1310_rx.c function and local names from CamelCase

Also renamed some items to improve readability, and other minor tidy-ups.
Tested on an ET-131x device.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>