check status of master links

def check_link_status():
    '''check status of master links'''
    tnow = time.time()
    if mpstate.status.last_message != 0 and tnow > mpstate.status.last_message + 5:
        say("no link")
        mpstate.status.heartbeat_error = True
    for master in mpstate.mav_master:
        if not master.linkerror and (tnow > master.last_message + 5 or master.portdead):
            say("link %u down" % (master.linknum+1))
            master.linkerror = True