One of the approaches for sniffing serial port communication on Windows
is using USBPcap, an open-source USB sniffer. When using Bluetooth as
the transport for DebugMux, the resulting PCAP contains RFCOMM frames,
which can later be analyzed using Wireshark.
This patch adds a new read-only DumpIO interface for sedbgmux-dump.py,
which allows one to parse and convert PCAPs containing DebugMux frames
encapsulated into BT RFCOMM packets.
PCAP parsing is easy thanks to pyshark  (new dependency).