MFC r298735

sfxge(4): do not use RxQ index as label

Labels are limitted by 32 on EF10. It is not sufficient on powerful hosts.
Since only one RxQ is running over each EvQ, zero label may be used.

Reviewed by: gnn
Sponsored by: Solarflare Communications, Inc.
PR: 208267
Differential Revision: https://reviews.freebsd.org/D6121