staging: r8188eu: Remove code depending on NAT25_LOOKUP

Remove all the code related to the management of the NAT25_LOOKUP
method in nat25_db_handle(). The only function that used that method was
the now deleted nat25_handle_frame(). Remove the NAT25_LOOKUP entry from
the NAT25_METHOD enum because it is not anymore used everywhere else in
the code of the driver.

Remove the 'sender' pointer to integer. Remove
__nat25_db_network_lookup_and_replace(). Following the deletion of the
code related to the NAT25_LOOKUP method, they are no more needed.

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20210817185723.15192-1-fmdefrancesco@gmail.com


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