wifi: mac80211: refactor populating mesh related fields in sinfo

Introduce the sta_set_mesh_sinfo() to populate mesh related
fields in sinfo structure for station statistics.
This will allow for the simplified population of other fields in the
sinfo structure for link level in a subsequent patch to add support
for MLO station statistics.
No functionality changes added.

Signed-off-by: Sarika Sharma <quic_sarishar@quicinc.com>
Link: https://patch.msgid.link/20250213171632.1646538-3-quic_sarishar@quicinc.com


[reword since it's just an internal thing]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>