iwlwifi: mvm: clean up invalid station handling

Using IWL_MVM_STATION_COUNT and IWL_INVALID_STATION together
isn't a good idea as they have different values. Always use
IWL_MVM_STATION_COUNT for an invalid station in MVM and move
the definition of the IWL_INVALID_STATION constant into the
DVM driver to avoid making such mistakes again. The one use
in the transport code can be hard-coded to -1 instead as the
station ID is passed as an integer there.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/pcie/tx.c

@@ -1063,7 +1063,7 @@ void iwl_trans_pcie_txq_enable(struct iwl_trans *trans, int txq_id, int fifo,
 		iwl_set_bits_prph(trans, SCD_QUEUECHAIN_SEL, BIT(txq_id));
 
 	/* If this queue is mapped to a certain station: it is an AGG queue */
-	if (sta_id != IWL_INVALID_STATION) {
+	if (sta_id >= 0) {
 		u16 ra_tid = BUILD_RAxTID(sta_id, tid);
 
 		/* Map receiver-address / traffic-ID to this queue */