Handle the case where during socket option processing, the user
switches a stack such that processing the stack specific socket
option does not make sense anymore. Return an error in this case.

MFC after:		1 week
Reviewed by:		markj
Reported by:		syzbot+a6e1d91f240ad5d72cd1@syzkaller.appspotmail.com
Sponsored by:		Netflix, Inc.
Differential revision:	https://reviews.freebsd.org/D30395