frame802154: comply with IEEE 802.15.4-2015 on PAN ID Field Handling

This patch changes the behaviors of frame802154_has_panid() for frames
of frame version 0b10 so that it complies with the PAN ID Field Handling
specification in IEEE 802.15.4-2015. For the other frame versions, 0b00
and 0b01, no change is made in frame802154_has_panid().

For more information, please refer to:
https://github.com/contiki-os/contiki/pull/1914/

regression-tests/25-ieee802154/js/01-panid-handling.js

@@ -0,0 +1,21 @@
+TIMEOUT(10000, log.testFailed());
+
+while(true) {
+    YIELD();
+
+    log.log(time + " " + id + " "+ msg + "\n");
+    
+    if(msg.contains("=check-me=") == false) {
+        continue;
+    }
+
+    if(msg.contains("FAILED")) {
+        log.testFailed();
+    }
+
+    if(msg.contains("DONE")) {
+        log.testOK();
+        break;
+    }
+    
+}