Add ICMP tap support, and add a tshark tap to measure such things as:

Add ICMP tap support, and add a tshark tap to measure such things as:
  * Number of ICMP echo requests, replies, lost replies and percent loss.
  * Min, Max, Average SRT (Service Response Time), and standard deviation.
(This is my first tap, so hopefully I didn't miss something, but we'll see ...)
TODO: Add a Wireshark tap.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@36480 f5534014-38df-0310-8fa8-9805f1628bb7