Add back the IP header length to the total packet length field on

Add back the IP header length to the total packet length field on
raw IP sockets.  It was deducted in ip_input() in preparation for
protocols interested only in the payload.

On raw sockets the IP header should be delivered as it at came in
from the network except for the byte order swaps in some fields.

This brings us in line with all other OS'es that provide raw
IP sockets.

Reported by: Matthew Cini Sarreo <mcins1-at-gmail.com>
MFC after: 3 days