Ensure that the report state is not a blocking call

Fixes bug 1191768

For the dhcp and l3 agents the first state report will be done
via a call. If this succeeds then subsequent calls will be done via
the cast method.

Change-Id: I82a1d92fc84983b7bb46758db0aee3e3eca1d3be
(cherry picked from commit 0407b59c259b2861b4541e31379e994ea8350b83)