net: ipc_router: Update the port_lock and define its hierarchy

Define the port_lock as a mutex and define its hierarchy so that any
out of order locking can be assessed through visual code inspection.

Change-Id: Ic0aedc99a4c912d91595d51bbebea2f99ed8952b
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>