Refactor isTetheringSupported() calls

Tethering currently wants access to complex isTetheringSupported
logic that is only available in ConnectivityService. Instead of
trying to access that via ConnectivityManager, pass this capability
in to Tethering directly, in the TetheringDependencies object.

Also:
    - ConnectivityManager is only a source of static constants now,
      so "import static" all the constants that are actually used.

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net works
    - manual USB towards WiFi tethering works
Bug: 68951715

Merged-In: Ifa121b057f9959ddb980edc940327929e48ea973
Merged-In: Iad6358dc2f1d10b322d22ec90543adc50882962d
Change-Id: Ia64faaadefb4a5d84a50da98bdebd544b6fda101
(cherry picked from commit 465ff3a0c1da8afd5cb13b25ed9a3c95ee0dd2c4)
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index 861ae83..a1ef1ed 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -910,7 +910,12 @@
 
     private Tethering makeTethering() {
         // TODO: Move other elements into @Overridden getters.
-        final TetheringDependencies deps = new TetheringDependencies();
+        final TetheringDependencies deps = new TetheringDependencies() {
+            @Override
+            public boolean isTetheringSupported() {
+                return ConnectivityService.this.isTetheringSupported();
+            }
+        };
         return new Tethering(mContext, mNetd, mStatsService, mPolicyManager,
                 IoThread.get().getLooper(), new MockableSystemProperties(),
                 deps);