The message dispatcher will only queue one message at a time for
both sending and downloading. On multi-sim scenarios this causes
failures in a subscription to delay all messages added after the
one that fails.
This patch changes the pending messages processor to queue one
message per subscription for both sending and received, instead of
one globally.
Test: m
Change-Id: Ia54906089dccbbe694aab7bf995ac08480d3e4f8
Ticket: CRACKLING-877
Diogo Ferreira