Support parsing RDNSS ND options from netlink.

The RDNSS options (RFC 6106) used to configure DNS servers via
router advertisements are passed from the kernel to userspace via
RTM_NEWNDUSEROPT netlink messages. Add code to NetlinkEvent to
parse them.

Also fix a compiler warning and a couple of style issues.

[Cherry-pick of b185e90dcc6ac111bff908edcc6d89fd6b37dc11]

Bug: 9180552
Change-Id: I6c532c8f0ceef3afdc977a431a036df398013e1a
diff --git a/include/sysutils/NetlinkEvent.h b/include/sysutils/NetlinkEvent.h
index f3501cf..c0a9418 100644
--- a/include/sysutils/NetlinkEvent.h
+++ b/include/sysutils/NetlinkEvent.h
@@ -36,6 +36,7 @@
     const static int NlActionLinkUp;
     const static int NlActionAddressUpdated;
     const static int NlActionAddressRemoved;
+    const static int NlActionRdnss;
 
     NetlinkEvent();
     virtual ~NetlinkEvent();
@@ -49,9 +50,10 @@
     void dump();
 
  protected:
-    bool parseIfAddrMessage(int type, struct ifaddrmsg *ifaddr, int rtasize);
     bool parseBinaryNetlinkMessage(char *buffer, int size);
     bool parseAsciiNetlinkMessage(char *buffer, int size);
+    bool parseIfAddrMessage(int type, struct ifaddrmsg *ifaddr, int rtasize);
+    bool parseNdUserOptMessage(struct nduseroptmsg *msg, int optsize);
 };
 
 #endif