Add averageRoundTripDelay rtp statistic

cdr/cdr_beanstalkd.c

cdr/cdr_csv.c

cdr/cdr_manager.c

cdr/cdr_odbc.c

cdr/cdr_radius.c

cdr/cdr_tds.c

channels/chan_brcm.c

include/asterisk/cdr.h

include/asterisk/channel.h

main/cdr.c