Support adding, deleting, and clearing IPv6 addrs.

- Provide a function to add and delete IPv4/IPv6 addresses
  using netlink.
- Provide a function that clears all IP addresses on an
  interface that can be used by netd.

Also, a couple of cleanups:

- Update the header file to match reality, and include the
  header file in the implementation. Also fix a caller that
  has an incorrect method signature.
- Fix whitespace in Android.mk.

Change-Id: Ifba9d60cdfffb0b7e5c3b9c6ab328f5f77d259c4
diff --git a/netcfg/netcfg.c b/netcfg/netcfg.c
index c520075..3738f24 100644
--- a/netcfg/netcfg.c
+++ b/netcfg/netcfg.c
@@ -50,8 +50,9 @@
 
 int dump_interface(const char *name)
 {
-    unsigned addr, prefixLength, flags;
+    unsigned addr, flags;
     unsigned char hwbuf[ETH_ALEN];
+    int prefixLength;
 
     if(ifc_get_info(name, &addr, &prefixLength, &flags)) {
         return 0;