DHCPv6: axe a couple invariant expressions

The "type > 65535" condition in dhcp6opt_name() was always false because
the function is given a 16-bit argument.

The "dh6->dh6_msgtype" condition in dhcp6_print() was always true
because name == NULL only when none of the preceding switch block cases
matched.
DHCPv6: make use of tok2str()
SCTP: use tok2str()
PIM: refresh and use tok2str()

Remove PIMv1 type 8 (Mode), which is missing from
draft-ietf-idmr-pim-spec-01 and is not decoded anyway.

List (w/o decoding) two PIMv2 types defined in 2007 and 2012.
IEEE 802.11: use tok2str()
OSPFv3: fix SEGV on SPARCv9 (concurs with 8f6bca3)

This bug arose on the OpenCSW build farm:

    ospf3_auth-vv                 : TEST FAILED

Dagobert Michelsen had helped to use the farm servers to debug.
remove unused function nfsreq_print()
PIM: add some v2 test cases

The sample captures come from packetlife.net through courtesy of Jeremy
Stretch.
NFS: use tok2str()
NDOize the rest of util.c
SMB: make use of tok2str() and ternary conditional
put Hannes' prior captures to work

Add test cases for the .pcap files added in 2005 (complements commits
279c3bd, 80d7284 and 0dcd9ac).
use more PacketLife captures for test cases

Improve coverage for ISAKMP, IGMP and HDLC. Add initial coverage for STP
variants, DECnet, RADIUS, DTP, LACP, LLDP, CDP, VTP and UDLD.
NFS: prepend %x format with 0x (mitigates GH #35)
fix runaway ND_PRINT() parentheses
Coverity: add the build script used by Travis-CI and Coverity Scan

from https://scan.coverity.com/scripts/travisci_build_coverity_scan.sh
Coverity: customize the build script

- add a 'Verify Coverity Scan run condition' step to avoid multiple runs with
  Travis matrix.
- add a 'Verify Coverity Scan script test mode' step. if true no uploading, to
  avoid reaching the quota. usual processing: false.
- send 'description' as VERSION#SHA (e.g.: 4.6.0-PRE-GIT#c661f8b)
Coverity: update .travis.yml for analysis by pushing in 'coverity_scan' branch
OSPFv3: add PacketLife sample captures
EIGRP: add IPv4 test cases from PacketLife