diag: Read and drop socket data when no fwd_ctxt available

Diag socket channel where no fwd_ctxt is available is not
reading data from socket when data is ready which is resulting
to memory allocation failure on ipc router side after multiple
SSR. The patch handles this case by reading and dropping the
data when it is available.

Change-Id: I631acce2946699e0a94d2510d46bf646ad117804
Signed-off-by: Hardik Arya <harya@codeaurora.org>