sctp: fix potential panics in the SCTP-AUTH API.

sctp: fix potential panics in the SCTP-AUTH API.

[ Upstream commit 5e739d1752aca4e8f3e794d431503bfca3162df4 ]

All of the SCTP-AUTH socket options could cause a panic
if the extension is disabled and the API is envoked.

Additionally, there were some additional assumptions that
certain pointers would always be valid which may not
always be the case.

This patch hardens the API and address all of the crash
scenarios.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>