net: dsa: tag_xrs700x: use the dsa_xmit_port_mask() helper

net: dsa: tag_xrs700x: use the dsa_xmit_port_mask() helper

The "xrs700x" is the original DSA tagging protocol with HSR TX
replication support, we now essentially move that logic to the
dsa_xmit_port_mask() helper. The end result is something akin to
hellcreek_xmit() (but reminds me I should also take care of
skb_checksum_help() for tail taggers in the core).

The implementation differences to dsa_xmit_port_mask() are immaterial.

Cc: George McCollister <george.mccollister@gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20251127120902.292555-15-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>