bpfmap: Move to Common Location

Move bpfmap to frameworks/libs/net/common/native.

Bug: 179733303
Change-Id: Id08b216ec6a64968d66d7990f91ea7ce222a1154
diff --git a/Tethering/proguard.flags b/Tethering/proguard.flags
index 75ecdce..f62df7f 100644
--- a/Tethering/proguard.flags
+++ b/Tethering/proguard.flags
@@ -4,7 +4,7 @@
     static final int EVENT_*;
 }
 
--keep class com.android.networkstack.tethering.BpfMap {
+-keep class com.android.networkstack.tethering.util.BpfMap {
     native <methods>;
 }