[CM] Unhide the NetworkSpecifier as object API

API visibility change: unhide allowing NetworkSpecifier
to be an arbitrary object.

Bug: 27533960
Bug: 36053921
Bug: 36275276
Test: builds and runs
Change-Id: I1d1705cca7ece077ef8d7c674c62d5369fedbb03

core/java/android/net/NetworkRequest.java

@@ -278,7 +278,6 @@ public class NetworkRequest implements Parcelable {
          *
          * @param networkSpecifier A concrete, parcelable framework class that extends
          *                         NetworkSpecifier.
-         * @hide
          */
         public Builder setNetworkSpecifier(NetworkSpecifier networkSpecifier) {
             MatchAllNetworkSpecifier.checkNotMatchAllNetworkSpecifier(networkSpecifier);