Refactor BpfNetMaps and getChainEnabled

Address comments from aosp/2117045 and aosp/2131752
Rename USE_NETD to PRE_T
Rename getChainEnabled to isChainEnabled
Remove unnecessary parentheses
Fix comment

Bug: 217624062
Test: atest BpfNetMapsTest
Change-Id: Iaff8c9fc5f74de3fe41a7fb010355b1742fbce90
diff --git a/framework/src/android/net/ConnectivityManager.java b/framework/src/android/net/ConnectivityManager.java
index 02083ff..eeedfd1 100644
--- a/framework/src/android/net/ConnectivityManager.java
+++ b/framework/src/android/net/ConnectivityManager.java
@@ -5922,7 +5922,7 @@
     }
 
     /**
-     * Get the specified firewall chain status.
+     * Get the specified firewall chain's status.
      *
      * @param chain target chain.
      * @return {@code true} if chain is enabled, {@code false} if chain is disabled.