sctp: propagate cap rights on sctp_peeloff
PR: 201052
Reviewed by: oshogbo, tuexen
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D46884
(cherry picked from commit 91a9e4e01dab7a740b8e3b7c39c59a537e71e5d2)