net: ipc_router: Defer workqueue initialization

IPC Router workqueue is initialized before some of the core IPC router
data structures are initialized leading to uninitialized data structure
access.

Initialize the workqueue after initializing the core data structures.

CRs-Fixed: 611234
Change-Id: Ia6fbd2f517afcde30b2c924507fbb9f28ccc01e3
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>