sfxge(4): fix RxQ structure layout vs usage on datapath

Recent changes in the pseudo header accessor prototypes start to
use common code RxQ handle on datapath. The handle was located
at the end of the structure with members not used on datapath.

Reviewed by: philip
Sponsored by: Solarflare Communications, Inc.
MFC after: 2 days
Differential Revision: https://reviews.freebsd.org/D9359