Ipdecap can decapsulate traffic encapsulated within GRE, IPIP, 6in4, and ESP (IPSEC) protocols, and can also remove IEEE 802.1Q (virtual LAN) headers. It reads packets from a pcap file, removes the encapsulation protocol, and writes them in another pcap file.
You can download it from the following link: https://packetstormsecurity.com/files/download/125536/ipdecap-0.7.tar.gz
Source: https://packetstormsecurity.com/files/125536/Ipdecap-0.7.html