public/io/netif.h: tidy up and remove duplicate comments

public/io/netif.h: tidy up and remove duplicate comments

Now that requests and response types and extra info segments are
documented in block comments, we can get rid of the inline comments
in the structures. This has the happy side-effect of making the Linux
checkpatch.pl script make fewer complaints after import.

This patch also fixes a small whitespace issue in the initial boiler-
plate comment, and a typo in one of the ascii-art diagrams.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>