receive: use gro call instead of plain call

[Jason A. Donenfeld]

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.

You might, by the way, be interested in using Flent for testing. It's
slightly more scientific, and its developer hangs out on this mailing
list.

https://flent.org/

Jason