I also use a CC2531. The only free and compatible software I found was TI's own Packet Sniffer application (the legacy version, not the newer PacketSniffer 2), but that is more or less unusable (does not decrypt messages, and UI is a mess). But it can broadcast the messages to network!
So I wrote an application that receives these messages, transforms them from TI's format to a Wireshark-supported protocol (ZEP), and sends these packets to localhost - so that I can easily capture them in Wireshark.
With this setup I only had to buy a CC2531 stick, and now I can sniff my network keys, store them in Wireshark, and all my Zigbee PANs are decrypted automatically... extremely convenient!
But it could be even more convenient if I could eliminate both Packet Sniffer and my tool, so in case anyone finds a way to integrate a cheap aliexpress CC2531 to wireshark directly, please let me know!