On some platforms, `msg.Attributes.Stats64` is `nil` because the kernel doesn't
expose 64-bit stats. In that case, return `msg.Attributes.Stats` instead, which
are the 32-bit equivalent.
Note that `RXOtherhostDropped` isn't available in that case, so we hardcode it
to zero.
Fixes#2756.
Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>
