configure: netinet/in_pcb.h and netinet/ip_var.h require netinet/in.h on Mac OS X.
diff --git a/configure b/configure
index efcf3ad..86adc79 100755
--- a/configure
+++ b/configure
@@ -7169,6 +7169,9 @@
      #if HAVE_SYS_SOCKETVAR_H
      # include <sys/socketvar.h>
      #endif
+     #if HAVE_NETINET_IN_H
+     # include <netinet/in.h>
+     #endif
 
 #include <$ac_header>
 _ACEOF