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.
print-ppp: fix "p[2] & 0x200 is always 0" found by Coverity and a bad shift
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.
.travis.yml: install libdnet-dev and libsmi2-dev devel libs
fix a couple typos
Merge remote-tracking branch 'bpf/master'