Enable IPv6 in the Windows build

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/configure b/configure
index 6baa579..78a6ccb 100755
--- a/configure
+++ b/configure
@@ -244,6 +244,7 @@
   output_sym "CONFIG_SCHED_IDLE"
   output_sym "CONFIG_TCP_NODELAY"
   output_sym "CONFIG_TLS_THREAD"
+  output_sym "CONFIG_IPV6"
   echo "CC=$CC" >> $config_host_mak
   echo "BUILD_CFLAGS=$CFLAGS -include config-host.h -D_GNU_SOURCE" >> $config_host_mak
   exit 0