fix: fix sipflow rtp recording

[yeoleobun]

This pull request contains following fix:

• Standard G722 does not support stereo, g722 recording does not work.
  • decode g722 to pcmu
• Remove the raw_packet.clone(), get the packet before transcoding.
• Since sipflow rtp decode need the header, use packet.mashal() instead of packet.payload, and useRtpPacket::parse instead of manually parse which assume fixed size header.
• Using zstd magic number predicate instead of compare the size. (the compressed data may have same size with the original)