wifi: iwlwifi: mvm: set properly mac header

In the driver we only use skb_put* for adding data to the skb, hence data
never moves and skb_reset_mac_haeder would set mac_header to the first
time data was added and not to mac80211 header, fix this my using the
actual len of bytes added for setting the mac header.

Fixes: 3f7a9d57

 ("wifi: iwlwifi: mvm: simplify by using SKB MAC header pointer")
Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240510170500.12f2de2909c3.I72a819b96f2fe55bde192a8fd31a4b96c301aa73@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>