msm: ipa: Add support to notify wan upstream iface info

Netmgr requires upstream iface info whenever tethering is
enabled to toggle RSB advanced feature on/off for the
respective upstream iface. Make changes to give provision
to get upstream iface whenever tethering is enabled.

Change-Id: I8f48f327ca55c3c91a978241087e6ffd5f8d4d10
Signed-off-by: Chaitanya Pratapa <cpratapa@codeaurora.org>