In that function the "length" parameter means off-the-wire length, that
is, the length declared inside the outer header. The "caplen" parameter
means the amount of bytes actually available in the captured packet.
gre_print_0() and the functions modelled after it passed the value of
"length" instead of the value of "caplen", this could make ether_print()
access beyond the memory allocated for the captured packet. Brian
Carpenter had demonstrated this for the OTV case.
Fix the involved functions that call ether_print() to pass the correct
value and leave a comment to dismiss "caplen" later as its value can be
reliably derived from the other ether_print() parameters.
Multiplying a uint8_t by an int results in an int, not an unsigned int;
make NSH_HDR_WORD_SIZE an unsigned constant so the multiplication is
uint8_t times unsigned int.
