receive: use gro call instead of plain call

[Lonnie Abelbeck]

> On Jul 13, 2018, at 1:27 PM, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
> 
> Hey Lonnie,
> 
> Wow, thanks for benching that (and watching the git repo for the
> experiment-of-the-day). This performance increase certainly exceeds my
> expectations; I'm quite pleased it's working so well.

Another huge improvement ...

pbx3: Intel(R) Celeron(R) CPU  N2930  @ 1.83GHz
      Ethernet controller: Intel Corporation I211

pbx:  Intel(R) Core(TM) i3-6100U CPU @ 2.30GHz
      Ethernet controller: Intel Corporation I211


pbx ~ # iperf3 -s

pbx3 ~ # iperf3 -c 10.4.0.10 -P2 -R
-- 0.0.20180625 --
[SUM]   0.00-10.03  sec   940 MBytes   786 Mbits/sec  251             sender
[SUM]   0.00-10.00  sec   933 MBytes   782 Mbits/sec                  receiver
-- 0.0.20180708 --
[SUM]   0.00-10.05  sec   730 MBytes   609 Mbits/sec  186             sender
[SUM]   0.00-10.01  sec   726 MBytes   608 Mbits/sec                  receiver
-- 0.0.20180708 w/napi_gro_receive patch --
[SUM]   0.00-10.04  sec   973 MBytes   813 Mbits/sec  289             sender
[SUM]   0.00-10.00  sec   969 MBytes   813 Mbits/sec                  receiver
--

Lonnie