DTLS/SCTP struct authchunks Bug

PR: 2809

DTLS/SCTP requires DATA and FORWARD-TSN chunks to be protected with
SCTP-AUTH.  It is checked if this has been activated successfully for
the local and remote peer. Due to a bug, however, the
gauth_number_of_chunks field of the authchunks struct is missing on
FreeBSD, and was therefore not considered in the OpenSSL implementation.
This patch sets the corresponding pointer for the check correctly
whether or not this bug is present.
(cherry picked from commit f596e3c491035fe80db5fc0c3ff6b647662b0003)