ice: Code optimization for ice_fill_sw_rule()

Use the buffer in the s_rule structure directly instead of using
a local array eth_hdr[DUMMY_ETH_HDR_LEN]

Signed-off-by: Zhenning Xiao <zhenning.xiao@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>