msgr: close shutdown race
msgr: close shutdown race

start the async callback inside msgr_init, so that there is no race
between starting the thread and shutting down the msgr.

Signed-off-by: Colin McCabe <3142ce8a0bdba4a38073365893e6b74f72d9c512@alumni.cmu.edu>

cmccabe/redfish,cmccabe/redfish,cmccabe/redfish,cmccabe/redfish,cmccabe/redfish