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: I1ee995528e6467fbe8e8e1b056acf7da52923a1c
Acked-by: Suhas Mallesh <smallesh@codeaurora.org>
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>