Netdissectify the to-name resolution routines.

Have them take a netdissect_options * argument, and get the "no name
resolution" flag from it.

Move the declaration of dnaddr_string to addrtoname.h, along with the
other XXX-to-string routines.
Define NETDISSECT_REWORKED and fix the issues it provokes.

I.e., use the flags from the netdissect_options structure.
Define NETDISSECT_REWORKED in a bunch of files, and fix the issues it finds.

The only one it found was that routines in sigsecret.c needed to refer
to ndo->ndo_sigsecret, not just sigsecret.
Declare default_print() only if NETDISSECT_REWORKED isn't defined.

Routines using netdissect_options should be using ndo->ndo_default_print.
fix a couple typos
Merge remote-tracking branch 'bpf/master'
PPTP: use tok2str() and ternary conditional
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.