rtl8187: Implement TX/RX blink for LED

The following patch implements some control over the LED on RTL8187B and
RTL8187L devices. Triggers are registered for TX and RX. Whenever the
trigger event occurs, the LED is turned off for 1/20 second, then turned
back on.

Note: For those RTL8187X devices that are built into the computer and have
a LED that is expected to be controlled with a radio switch, this patch will
not operate that LED. That will take a separate patch to be prepared later.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
Tested-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>