Put the LINUX_SLL_P_ definitions back, and check for at least some of

Put the LINUX_SLL_P_ definitions back, and check for at least some of
them in "print-sll.c" - as a cooked-mode capture may be reading from
non-Ethernet, non-802.x devices, it may well see some
ETH_P_/LINUX_SLL_P_ types that don't mean "this is an 802.2 LLC frame".

We currently assume that the ETH_P_ values won't change in the kernel,
so we don't have to explicitly map them.

In various link-layer packet printers, if we don't handle the next layer
up of packet type, and are printing the link-layer header, use the
correct pointer to that header (i.e., if we've stepped "p" past the
link-layer header, don't use "p", use a pointer to the beginning of the
packet), and use the correct length (i.e., if we've subtracted the
length of the link-layer header, add it back in, so that we always print
the full packet length).