staging: r8188eu: core: remove the function __nat25_timeout

Remove the function __nat25_timeout from rtw_br_ext.c file. This function
can be replace by single statement jiffies - NAT25_AGEING_TIME*HZ.

Signed-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Link: https://lore.kernel.org/r/YYNJPCQ5hX8BTzwy@Sauravs-MacBook-Air.local


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>