staging: rtl8712: Replace function r8712_free_network_queue

Remove function r8712_free_network_queue, as it does nothing but call
_free_network queue; rename _free_network_queue to
r8712_free_network_queue to enable continued functionality; change the
type of r8712_free_network_queue (formerly _free_network_queue) from
static to non-static to match the type of the old
r8712_free_network_queue.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>