Fix rt_msghdr padding on NetBSD.

NetBSD uses a fixed 64-bit padding, unlike OS X (32-bit), and unlike
other platforms (sizeof(unsigned long)). There is an RT_ROUNDUP macro
that does the right alignment; use that when available.

http://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/lib/libc/net/getifaddrs.c
http://fxr.watson.org/fxr/source/net/route.h?v=NETBSD#L270

Rounding to 4 bytes was breaking with IPv6 addresses, which are 28
bytes. The pointer was being advanced by 28 instead of 32. Compare to
r29739, somewhat similar.

Reported by Fredrik Pettai.
http://seclists.org/nmap-dev/2013/q1/384

CHANGELOG

@@ -1,5 +1,7 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o Fixed IPv6 routing table alignment on NetBSD.
+
 o [NSE] Added http-phpmyadmin-dir-traversal by Alexey Meshcheryakov.
 
 o Added a service probe for Erlang distribution nodes.

libdnet-stripped/NMAP_MODIFICATIONS

@@ -1887,3 +1887,26 @@ index 4fe059c..184c077 100644
  		/* XXX - why must this happen before SIOCSIFADDR? */
  		if (addr_btos(entry->intf_addr.addr_bits,
  		    &ifr.ifr_addr) == 0) {
+
+o Use the RT_ROUNDUP preprocessor macro for 64-bit rt_msghdr alignment
+  on NetBSD.
+
+diff --git a/libdnet-stripped/src/route-bsd.c b/libdnet-stripped/src/route-bsd.c
+index 44e7dd2..47f3705 100644
+--- a/libdnet-stripped/src/route-bsd.c
++++ b/libdnet-stripped/src/route-bsd.c
+@@ -47,8 +47,14 @@
+ 
+ #include "dnet.h"
+ 
++#ifdef RT_ROUNDUP
++/* NetBSD defines this macro rounding to 64-bit boundaries.
++   http://fxr.watson.org/fxr/ident?v=NETBSD;i=RT_ROUNDUP */
++#define ROUNDUP(a) RT_ROUNDUP(a)
++#else
+ #define ROUNDUP(a) \
+ 	((a) > 0 ? (1 + (((a) - 1) | (RT_MSGHDR_ALIGNMENT - 1))) : RT_MSGHDR_ALIGNMENT)
++#endif
+ 
+ #ifdef HAVE_SOCKADDR_SA_LEN
+ #define NEXTSA(s) \

libdnet-stripped/src/route-bsd.c

@@ -47,8 +47,14 @@
 
 #include "dnet.h"
 
+#ifdef RT_ROUNDUP
+/* NetBSD defines this macro rounding to 64-bit boundaries.
+   http://fxr.watson.org/fxr/ident?v=NETBSD;i=RT_ROUNDUP */
+#define ROUNDUP(a) RT_ROUNDUP(a)
+#else
 #define ROUNDUP(a) \
 	((a) > 0 ? (1 + (((a) - 1) | (RT_MSGHDR_ALIGNMENT - 1))) : RT_MSGHDR_ALIGNMENT)
+#endif
 
 #ifdef HAVE_SOCKADDR_SA_LEN
 #define NEXTSA(s) \