intel_avf: fix rx/tx packet lengths
intel_avf: fix rx/tx packet lengths

This fixes a bug originally introduced in fece51f0 where sent packets
where with 4 bytes too many as a trailer.

Reverts the hence bogus 355051b0.

The original bug I believe comes from a misunderstood shift truncation
which is fixed by a 0ULL+ before shift.
The original 4ULL+ "fix" was likely a fever dream of mine where I
thought AVF expects us to specify the packet size+4 (i.e., include
space for the CRC?), and only fixed the real issue (shift truncation) by
accident.

eugeneia/snabb,SnabbCo/snabbswitch,eugeneia/snabb,SnabbCo/snabbswitch,snabbco/snabb,snabbco/snabb,snabbco/snabb,snabbco/snabb,eugeneia/snabb,snabbco/snabb,Igalia/snabb,snabbco/snabb,Igalia/snabb,Igalia/snabb,Igalia/snabb,Igalia/snabb,Igalia/snabb,SnabbCo/snabbswitch,eugeneia/snabb,SnabbCo/snabbswitch,eugeneia/snabb,snabbco/snabb,eugeneia/snabb,eugeneia/snabb,eugeneia/snabb,Igalia/snabb,snabbco/snabb,Igalia/snabb