sctp: change to use TCP_CLOSE_WAIT as SCTP_SS_CLOSING

Prior to this patch, sctp defined TCP_CLOSING as SCTP_SS_CLOSING.
TCP_CLOSING is such a special sk state in TCP that inet common codes
even exclude it.

For instance, inet_accept thinks the accept sk's state never be
TCP_CLOSING, or it will give a WARN_ON. TCP works well with that
while SCTP may trigger the call trace, as CLOSING state in SCTP
has different meaning from TCP.

This fix is to change to use TCP_CLOSE_WAIT as SCTP_SS_CLOSING,
instead of TCP_CLOSING. Some side-effects could be expected,
regardless of not being used before. inet_accept will accept it
now.

I did all the func_tests in lksctp-tools and ran sctp codnomicon
fuzzer tests against this patch, no regression or failure found.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>