rtwn: fix mbuf allocation errors in USB RX path for > 4 KiB frames

[adrian]

Summary

We can and do receive > 4 KiB frames in the RX path (A-MSDU frames
can be up to 11KiB.) At least one user has reported seeing this
and having it break their traffic flows.

Use m_get3() to try and grab an mbuf jumbo cluster.

This may not be the best permanent solution, but it at least will
fail for frame sizes we expect to see up and including the largest
A-MPDU frame (11Kib) and keep a counter if it can't allocate, versus
just returning NULL because it's too large (and not keeping counters.)

PR: kern/286366

[bz]

If you don't want to add totlen to the printf consider this Accepted.

sys/dev/rtwn/usb/rtwn_usb_rx.c

131

I start to disklike mbufs more and more. I'll need the same change in LinuxKPI. Thanks!

133

What would really be helpful for immediate debugging is to also print totlen in that statement.

[adrian]

add totlen, on suggestion from bz@