staging: octeon-ethernet: make dropped packets to consume NAPI budget

We should count also dropped packets, otherwise the NAPI handler may
end up running too long.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: devel@driverdev.osuosl.org
Cc: linux-mips@linux-mips.org
Cc: David Daney <david.daney@cavium.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: richard@nod.at
Patchwork: https://patchwork.linux-mips.org/patch/5809/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>