ipc: stop async IPC loop on callback request

ipc: stop async IPC loop on callback request

EAL did not stop processing further asynchronous requests on
encountering a request that should trigger the callback. This
resulted in erasing valid requests but not triggering them.

Fix this by stopping the loop once we have a request that
can trigger the callback. Once triggered, we go back to scanning
the request queue until there are no more callbacks to trigger.

Fixes: f05e26051c15 ("eal: add IPC asynchronous request")
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Jianfeng Tan <jianfeng.tan@intel.com>