wil6210: account for napi_gro_receive never returning GRO_DROP

The napi_gro_receive function no longer returns GRO_DROP ever, making
handling GRO_DROP dead code. This commit removes that dead code.
Further, it's not even clear that device drivers have any business in
taking action after passing off received packets; that's arguably out of
their hands. In this case, too, the non-gro path didn't bother checking
the return value. Plus, this had some clunky debugging functions that
duplicated code from elsewhere and was generally pretty messy. So, this
commit cleans that all up too.

Fixes: 6570bc79

 ("net: core: use listified Rx for GRO_NORMAL in napi_gro_receive()")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>