drivers: net: rmnet: Check if SHS reports slow start

SHS module will proactively check to see if we are
in slow start mode. If we are then we can return true
to whoever asks.

Change-Id: Ia0e600207b2ff7fc4789006c7fcc6861908480a3
Signed-off-by: Conner Huff <chuff@codeaurora.org>