When a keepalive timeout occurs keepalive_retry_cnt remains zero,
so when the connection is re-established _on_keepalive_evt will
immediately disconnect instead of actually sending a keepalive ping.
The sequence looks like:
1. _on_connack: start con->keepalive_timer
2. Server does not respond to keepalive pings
3. _on_keepalive_evt: con->keepalive_retry_cnt reaches zero
4. Connection torn down and ASYMCUTE_DISCONNECTED sent to application
5. Application starts reconnection
6. _on_connack: start con->keepalive_timer again
7. First _on_keepalive_evt: con->keepalive_retry_cnt is still zero
8. Repeat from 4.
So this simply resets keepalive_retry_cnt in _on_connack when
the keepalive timer is restarted. It's a new connection, so
resetting the keepalive retry counter make senses regardless.
Signed-off-by: Derek Hageman <hageman@inthat.cloud>
18910cf4e2