msm: ipa: support initialization of multiple tethering protocols

Add support to initialization of multiple tethering protocols.
Each protocol initialized can register specific user_data that will
be used for notifications to USB driver.
The user_data that is used for the notifications is the one registered
for the current connected protocol.

Change-Id: I386af5ee0444545203508180de720a58b465bc1c
Signed-off-by: Sivan Reinstein <sivanr@codeaurora.org>