tcpdump.c. Have if_print routines return the length of the link-layer
header, so that the common code knows how to skip the link-layer header
when printing the packet in hex/ASCII.
unused-parameter problems reported by GCC. Add an _U_ tag to label
parameters as unused if the function is called through a pointer (so
that you can't change its signature by removing parameters) or if there
are unused parameters only because the function isn't complete.
Add some additional bounds checks the necessity for which was revealed
while cleaning up unused-parameter problems.
Make some routines static.
"lcp_print()", defined in "print-lcp.c", isn't called anywhere -
"print-ppp.c" has the code to dissect LCP. Get rid of "print-lcp.c".
