r8169: make rtl_rx better readable

Avoid the goto from the rx error handling branch into the else branch,
and in general avoid having the main rx work in the else branch.
In addition ensure proper reverse xmas tree order of variables in the
for loop.

No functional change intended.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>