socket: Annotate sooptcopyin() and sooptcopyout() with __result_use_check

Just like we do with copyin() and copyout().

Reviewed by: glebius
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D53114

(cherry picked from commit 3509dcd11a982107d957b99f6740704e9c522bd8)