CodingStyle: add networking specific block comment style

The block comment style in net/ and drivers/net is non-standard.
Document it.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: "Allan, Bruce W" <bruce.w.allan@intel.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>