New port: net/ipdecap

Decapsulate traffic encapsulated within GRE, IPIP, 6in4 and ESP protocols
from a pcap file.

Can also remove IEEE 802.1Q (virtual lan - vlan) header.

WWW: https://loicpefferkorn.net/ipdecap/

PR: 208993
Submitted by: Loic Pefferkorn <loic-freebsd@loicp.eu>