The SYSCTL data pointers can come from userspace and must not be
directly accessed. Although this will work on some platforms, it can
throw an exception if the pointer is invalid and then panic the kernel.

Add a missing SYSCTL_IN() of "SCTP_BASE_STATS" structure.

MFC after:	3 days
Sponsored by:	Mellanox Technologies


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273773 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f