Have print_llc() clear out the extracted_ethertype argument, rather than

Have print_llc() clear out the extracted_ethertype argument, rather than
having its callers do so - some of its callers *weren't* doing so,
leaving random junk in that argument in some cases.

When checking for "802.3-encapsulated" IPX, check the raw values of the
SSAP and DSAP for 0xFF, don't check them after the low-order bit has
been masked off.

The "flag" values in the LLC header aren't bits, they're combinations of
bits, including the combination "no bits"; don't use "bittok2str()" on
them.  Also, combine the proper bits, namely the C/R bit (which we
weren't combining) and the P/F bit (which we were).