wifi: Add a StaWifiMac method to get the link ID as set by the AP

src/wifi/model/sta-wifi-mac.cc

@@ -772,6 +772,12 @@ StaWifiMac::GetSetupLinkIds() const
     return linkIds;
 }
 
+std::optional<uint8_t>
+StaWifiMac::GetApLinkId(uint8_t linkId) const
+{
+    return GetLink(linkId).apLinkId;
+}
+
 Mac48Address
 StaWifiMac::DoGetLocalAddress(const Mac48Address& remoteAddr) const
 {

src/wifi/model/sta-wifi-mac.h

@@ -233,6 +233,12 @@ class StaWifiMac : public WifiMac
      */
     std::set<uint8_t> GetSetupLinkIds() const;
 
+    /**
+     * \param linkId the IO of the given link
+     * \return the ID (as set by the AP) of the given link, if the given link has been setup
+     */
+    std::optional<uint8_t> GetApLinkId(uint8_t linkId) const;
+
     /**
      * Return the association ID.
      *