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/Makefile.am b/Makefile.am
index 0cd75be..3dea489 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,10 +1,10 @@
 ## Process this file with automake to produce Makefile.in.
 
-SUBDIRS = lib qpb fpm @ZEBRA@ @BGPD@ @RIPD@ @RIPNGD@ @OSPFD@ @OSPF6D@ \
+SUBDIRS = lib qpb fpm @ZEBRA@ @BGPD@ @RIPD@ @RIPNGD@ @OSPFD@ @OSPF6D@ @NHRPD@ \
          @ISISD@ @PIMD@ @WATCHQUAGGA@ @VTYSH@ @OSPFCLIENT@ @DOC@ m4 @pkgsrcdir@ \
          redhat @SOLARIS@ tests
 
-DIST_SUBDIRS = lib qpb fpm zebra bgpd ripd ripngd ospfd ospf6d \
+DIST_SUBDIRS = lib qpb fpm zebra bgpd ripd ripngd ospfd ospf6d nhrpd \
 	  isisd watchquagga vtysh ospfclient doc m4 pkgsrc redhat tests \
 	  solaris pimd