net: ipc_router: Split IPC Router initialization

IPC Router initializes its core data structures along with its user-space
interface related data structures. Since the clients can interface with IPC
Router from different context, initialize the core data structures
separately from the interface and keep the core initialization sequence
light-weight.

Change-Id: I267cc8d376e7531975603d9308349cf4986a81e9
Signed-off-by: Atish Kumar Patra <apatra@codeaurora.org>