ice: Do not set LB_EN for prune switch rules

LB_EN for prune switch rules was causing all TX traffic
to loopback to the internal switch and dropped.  When
running bi-directional stress workloads with RDMA
the RDPU would hang blocking tx and rx traffic.

Signed-off-by: Christopher N Bednarz <christopher.n.bednarz@intel.com>
Reviewed-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>