This allows a big swath of ifdefs to be removed. It also means savings as the db var is not passed around all of the time, and makes it easier to remove the final broker call to mosquitto_time() call in packet_mosq.c. In one test this reduced the calls to mosquitto_time() from 295k to 48k.
keep v5 client read test to test for backwards compatability
adds username="usrname" and listener_port=1883 for v6 tests
Signed-off-by: david-beinder <david.beinder@mce.li>
This includes changes to improve read/write performance.
It is not complete, and will have further changes to add properties and anything else required for MQTT v5.
