A philosophical point that loopback is supposed to faithfully mirror
the same processing done for physical interfaces, else there's a whole
lot more you can cut out, like TCP retransmissions and TCP out-of-order
reassembly.

A stylistic suggestion to add a IFF_LOOPBACK_SKIP_*_SUM flag that's set
on the loopback interface when the *_do_loopback_cksum sysctls are
turned on or off.  Then you can just do one check instead of two in
all the conditional added.

							Jeffrey