MFC r333382:

When reporting ERROR or ABORT chunks, don't use more data
that is guaranteed to be contigous.
Thanks to Felix Weinrank for finding and reporting this bug
by fuzzing the usrsctp stack.

MFC r333386:

Fix two typos reported by N. J. Mann, which were introduced in
https://svnweb.freebsd.org/changeset/base/333382 by me.

Approved by: re@ (marius)