msm: ipa: support ioctl about upstream wan iface

CnE in user-space will ioctl ipa-driver to
inform which interface is the updtream WAN
iface and IPACM will set default route
based on this info.

Change-Id: I2b2aa5b52e91ad750ce66e1a897144e80714165d
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>