freetds: enable odbcSupport by default

There is no reason not to, and some packages which I'm working on,
requires this.

pkgs/development/libraries/freetds/default.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchurl, autoreconfHook, pkgconfig
 , openssl
-, odbcSupport ? false, unixODBC ? null }:
+, odbcSupport ? true, unixODBC ? null }:
 
 assert odbcSupport -> unixODBC != null;