proc: switch /proc/irda/irnet to seq_file interface

Probably interface misuse, because of the way iterating over hashbin is done.
However! Printing of socket number ("IrNET socket %d - ", i++") made conversion
to proper ->start/->next difficult enough to do blindly without hardware.
Said that, please apply.

Remove useless comment while I am it.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: Samuel Ortiz <samuel@sortiz.org>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>