hsic: rmnet: Support GET EPID IOCTL

this ioctl is required to bind rmnet physical channel to logical
channel. usb rmnet interface number will be used for that binding.

Change-Id: I4ccde7e9f8373921aa95c6a3a358707474f9865f
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>