fixup credits

A recent commit replaced tcpdump contributors list  with libpcap
contributors list and added to the replaced list new libpcap
contributors. Restore the original list and add new tcpdump
contributors:

* Bram
* Dmitrij Tejblum
* fra
* Gregory Detal
* Jorge Boncompte [DTI2]
* Longinus00
* Marc Abramowitz
* Ola Martin Lykkja
* Oleksij Rempel
* Petar Alilovic
* Stephane Bortzmeyer
* Thomas Jacob
* Udayakumar
* Wim Torfs

Fix some sorting and formatting while at it.
print-ip6: add a test on the header version value
AHCP: add version 1 decoder

Add new decoder for UDP port 5359 and a sample packet capture produced
on a couple of Linux hosts (a server and a client). Besides that, an
existing Babel capture contained AHCP packets and the current AHCP tests
cover 0, 1 and 2 "-v" flags.
AHCP: designated inits are C99, fix to be C89
remove unused macro from sctpHeader.h
Fix compilation warnings:
- set but unused variables
- type punned casts
Fix compilation warnings: set but unused variables.
remove two needless macros

ETH_ALEN in print-rrcp.c was unused. OFP_ETH_ALEN in
print-openflow-1.0.c was a reinvention of ETHER_ADDR_LEN.
AHCP: fix compiling w/o IPv6
add more tests to Travis build

Build with two compilers instead of one, test with and without IPv6.
skip "make check" for Travis builds w/o IPv6

tcpdump can build w/o IPv6 but its output will differ in many test
cases. Make sure test cases are only used with IPv4+IPv6 builds.
Merge pull request #344 from glebius/master

Fix several compilation warnings
OpenFlow 1.0: add OFPT_VENDOR messages test case

This capture was produced using an Arista DCS-7050Q-16 switch running
EOS-4.10.4 software. The controller sends two vendor messages
(BSN_GET_IP_MASK_REQUEST and BSN_GET_MIRRORING_REQUEST) and the switch
sends a reply for each (BSN_GET_IP_MASK_REPLY and
BSN_GET_MIRRORING_REPLY respectively).