[SCTP]: Convert sctp_dbg_objcnt to seq files.

This makes the code use a good proc API and the text ~50 bytes shorter.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>