Switch back to subsystem "net" for netlink events.

The change to enable address tracking via netlink incorrectly
changed the subsystem of rtnetlink events from "net" to
"interface". This broke interface add/delete notifications,
which come from the kernel with subsystem "net".

Switch back to "net" and deal with address tracking via new
action codes instead of a new subsystem.

[Cherry-pick of f34861346d5c207912075fba9874090e4c947869]

Bug: 10433320
Change-Id: Ibf30efb426949dfd02304cc1d9adb1c005a539a6
diff --git a/include/sysutils/NetlinkEvent.h b/include/sysutils/NetlinkEvent.h
index 2a734cb..f3501cf 100644
--- a/include/sysutils/NetlinkEvent.h
+++ b/include/sysutils/NetlinkEvent.h
@@ -34,6 +34,8 @@
     const static int NlActionChange;
     const static int NlActionLinkDown;
     const static int NlActionLinkUp;
+    const static int NlActionAddressUpdated;
+    const static int NlActionAddressRemoved;
 
     NetlinkEvent();
     virtual ~NetlinkEvent();