scons: Add use_tuntap to export list

Fixes broken build after c58537c.

Change-Id: I686ffaaad4fe558b6e51c89c9b26121318c2b721
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/3647
Reviewed-by: Gabe Black <gabeblack@google.com>
1 file changed