nhrpd: implement next hop resolution protocol

This provides DMVPN support and integrates to strongSwan. Please read
README.nhrpd and README.kernel for more details.
diff --git a/lib/log.h b/lib/log.h
index 7aa0896..59968ae 100644
--- a/lib/log.h
+++ b/lib/log.h
@@ -24,6 +24,7 @@
 #define _ZEBRA_LOG_H
 
 #include <syslog.h>
+#include <stdio.h>
 
 /* Here is some guidance on logging levels to use:
  *
@@ -54,7 +55,8 @@
   ZLOG_OSPF6,
   ZLOG_ISIS,
   ZLOG_PIM,
-  ZLOG_MASC
+  ZLOG_MASC,
+  ZLOG_NHRP,
 } zlog_proto_t;
 
 /* If maxlvl is set to ZLOG_DISABLED, then no messages will be sent