improve some recent conversions
NDOize Juniper DLT decoders
NDOize SNMP decoder
amend previous commit to fix compiling with libsmi
NDOize RX decoder
squelch compiler warnings after previous commit

It was OK with GCC but Clang wants <stdlib.h> back because of malloc()
and free() that shouldn't be declared implicitly.
Fix some unsafe print calls.

The format argument to a printf-like routine should either be a constant
string or a variable *known* to point to a format string.  It should not
be an arbitrary string you're trying to print - if that string contains
% characters, they will be interpreted as part of a format
specification, which can cause crashes (e.g., "%s", if what appears to
be an argument corresponding to that %s, when interpreted as a pointer,
doesn't point to a valid string) or other incorrect behavior.

If you want to print a string, use "%s" as the format and the string as
the argument.
Add support for Apple's DLT_PKTAP.