Add packet direction flag

[NDStrahilevitz]

In order to implement #3697 on top of TCP packet, and since it's useful information in general, the ingress/egress direction of packets should be added to the net_packet family of events.

This can be added either as an argument to all these events, or it should be added to a new Network context section.
If it's decided that a section should be added instead, it's likely more "correct" to move the following arguments there as well: src, dst, src_port, src_dst.