TetheringManager API clean up

Per API review:
- @IntDef defined on the type integer parameter
- have getters on each parameter that is set in the
  TetheringRequest.Builder
- new added API should not be deprecated
Below APIs is moved from system-current to module-lib-current that only
plafrom code(e.g. ConnectivityManager and Settings) can use them.
TetheringRequest.
onTetherableInterfaceRegexpsChanged, TetheringInterfaceRegexps:
Only platform code can use them because interfaces by regular
expressions are a mechanism which is planning to be deprecated.

Also rename some constants for easier to understand.

Bug: 149858697
Bug: 151243337
Test: m doc-comment-check-docs
      atest TetheringTests
Change-Id: I45cb21d5bc919f6d32c42650326597d5173ea028
Merged-In: Idd041f0fbeca411ea23e49786a50dd7feb77ef45

Tethering/src/android/net/ip/IpServer.java

@@ -1054,7 +1054,7 @@ public class IpServer extends StateMachine {
                 case CMD_START_TETHERING_ERROR:
                 case CMD_STOP_TETHERING_ERROR:
                 case CMD_SET_DNS_FORWARDERS_ERROR:
-                    mLastError = TetheringManager.TETHER_ERROR_MASTER_ERROR;
+                    mLastError = TetheringManager.TETHER_ERROR_INTERNAL_ERROR;
                     transitionTo(mInitialState);
                     break;
                 default:
@@ -1185,7 +1185,7 @@ public class IpServer extends StateMachine {
                         } catch (RemoteException | ServiceSpecificException e) {
                             mLog.e("Exception enabling NAT: " + e.toString());
                             cleanupUpstream();
-                            mLastError = TetheringManager.TETHER_ERROR_ENABLE_NAT_ERROR;
+                            mLastError = TetheringManager.TETHER_ERROR_ENABLE_FORWARDING_ERROR;
                             transitionTo(mInitialState);
                             return true;
                         }