Replace FIRST_SDK_INT to DEVICE_INITIAL_SDK_INT in Connectivity

Replace all FIRST_SDK_INT usage in Connectivity because it has
been renamed to DEVICE_INITIAL_SDK_INT.

Bug: 184735771
Test: m CtsNetTestCases
Ignore-AOSP-First: Some files are differnet between aosp and
                   sc-dev on frameworkrs/base.
Change-Id: I2f155592b08cdbf259a00b035cacb37ca9847e72

tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java

@@ -1398,7 +1398,7 @@ public class ConnectivityManagerTest {
             return;
         }
 
-        final int firstSdk = Build.VERSION.FIRST_SDK_INT;
+        final int firstSdk = Build.VERSION.DEVICE_INITIAL_SDK_INT;
         if (firstSdk < Build.VERSION_CODES.Q) {
             Log.i(TAG, "testSocketKeepaliveLimitTelephony: skip test for devices launching"
                     + " before Q: " + firstSdk);