staging: et131x: Create et131x_[dis|en]able_txrx() calls

In et131x_netdev.c, a series of calls to enable and diasble the rx/tx engine and queue are being used in several different places.
Create two functions to encapsulate these calls, and replace many calls with just the one.

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