Re-enable "Download" if auto-download is off

Messaging will skip downloading of Mms if auto-download
is off. Re-enable "Download" to let user can retry to
download manually.

Change-Id: I0b7b4c6b5ea1428e390fc3fc87832a89cb3821c9
Signed-off-by: Roger Chen <cxr514033970@gmail.com>