Call log fixes for getting RTP stats

This commit includes 3 fixes:
- change place of get/set rtp statistics to have them properly updated in cdr
for both incoming and outgoing call
- do not create additional "hangup" call log record
- save rtp stats counters from endptmngr into brcm_subchannel instead of
one global structure to support concurrent calls simultaneously

Signed-off-by: Grzegorz Sluja <grzegorz.sluja@iopsys.eu>