res_rtp_asterisk: Fix bug in function CHANNEL(rtcp, all_rtt)

Function CHANNEL(rtcp,all_rtt) CHANNEL(rtcp,all_loss) CHANNEL(rtcp,all_jitter)
always return 0.0 due to wrong define of macro "AST_RTP_SATA_SET" and
"AST_RTP_STAT_STRCPY".
It should compare "combined" with "stat" not "current_stat".

ASTERISK-26710 #close
Reported-by: Aaron An
Tested-by: AaronAn

Change-Id: Id4140fafbf92e2db689dac5b17d9caa009028a15