This patch fixes the PCAP logging. If frames are received from E1
interface, an 8 byte mISDN header (MISDN_HEADER_LEN) is in front of the
RSL packet. When frames are transmitted to the E1 interface, the
pcap_write_packet function will get a message buffer without the mISDN
header in front of the RSL packet. The pcap file was tested and the
output is correct.