msm:ipa: Request QMI BW indication only when tethering is enabled

This change allows Q6 to send QMI bandwidth changes to APQ only when
tethering is enabled.

Change-Id: Ie04eb11efd90af28065fd1c0842cb99b81e9ebad
Acked-by: Suhas Mallesh <smallesh@qti.qualcomm.com>
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>