isakmp: note why we include ipproto.h.

We don't use any IPPROTO_ values, but we *do* use netdb_protoname(),
which is declared in ipproto.h (because it's defined in ipproto.c).

Author: guyharris

print-isakmp.c

@@ -55,7 +55,7 @@
 
 #include "ip.h"
 #include "ip6.h"
-#include "ipproto.h"
+#include "ipproto.h"	/* for netdb_protoname() */
 
 typedef nd_byte cookie_t[8];
 typedef nd_byte msgid_t[4];