Include netinet/in.h (if detected) in check for net/pfvar.h

Patch from rubiate; fixes bug 17551.

changes/bug17551

+  o Minor bugfixes (compilation):
+    - When checking for net/pfvar.h, include netinet/in.h if possible.
+      This fixes transparent proxy detection on OpenBSD. Fixes bug
+      17551; bugfix on 0.1.2.1-alpha. Patch from "rubiate".

configure.ac

@@ -971,6 +971,9 @@ AC_CHECK_HEADERS(net/pfvar.h, net_pfvar_found=1, net_pfvar_found=0,
 #endif
 #ifdef HAVE_NET_IF_H
 #include <net/if.h>
+#endif
+#ifdef HAVE_NETINET_IN_H
+#include <netinet/in.h>
 #endif])
 
 AC_CHECK_HEADERS(linux/if.h,[],[],