Do not allow L2CAP specifier with ROLE_SERVER and remote address set

This is an invalid combination that never seems useful. Note that this
still allows ROLE_ANY in combination with a remote address. This still
doesn't seem particularly useful, but there is no good reason to
disallow it.

Test: TH
Change-Id: Ib0b7284cb99ee92f14113f8184af978eeb2318e7

framework/src/android/net/L2capNetworkSpecifier.java

@@ -240,7 +240,10 @@ public final class L2capNetworkSpecifier extends NetworkSpecifier implements Par
         /** Create the L2capNetworkSpecifier object. */
         @NonNull
         public L2capNetworkSpecifier build() {
-            // TODO: throw an exception for combinations that cannot be supported.
+            if (mRole == ROLE_SERVER && mRemoteAddress != null) {
+                throw new IllegalArgumentException(
+                        "Specifying a remote address is not valid for server role.");
+            }
             return new L2capNetworkSpecifier(mRole, mHeaderCompression, mRemoteAddress, mPsm);
         }
     }