Cosmetic early RTP sending issue and please test

Hi, before the l1sap changes were merged I fixed a case where after a ip.access CRCX with recvonly mode the BTS would already start to send RTP frames to UDP port 0 which will trigger an ICMP unreachable. This is not harmful but still a bug. After the l1sap merge the sysmobts is still doing it when it receives a TCH frame and all other bts models behave like before the bugfix. The below diff copies this into the common code. Besides administratives work I try to work on the SMSC, so if anyone could testdrive this patch and check for ICMP errors it would be greatly appreciated. holger