sctp: add transport state in /proc/net/sctp/remaddr

It is often quite helpful to be able to know the state of a transport
outside of the application itself (for troubleshooting purposes or for
monitoring purposes). Add it under /proc/net/sctp/remaddr.

Signed-off-by: Michele Baldessari <michele@acksyn.org>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>