[RFCLAT#10] remove libnl related files

libnl is not required anymore. remove all related files.

Bug: 212345928
Test: atest clatd_test and manual test
1. Connect to ipv6-only wifi.
2. Try IPv4 traffic.
   $ ping 8.8.8.8

Change-Id: Ic4725ef01667576f2a958f38d458374c2e749569
diff --git a/getaddr.c b/getaddr.c
index f25efc1..ba8052d 100644
--- a/getaddr.c
+++ b/getaddr.c
@@ -22,8 +22,7 @@
 #include <linux/rtnetlink.h>
 #include <net/if.h>
 #include <netinet/in.h>
-#include <netlink/handlers.h>
-#include <netlink/msg.h>
+#include <stdlib.h>
 #include <string.h>
 #include <strings.h>
 #include <unistd.h>