Mfp: r296345

No need to keep type stability on raw sockets zone.
We've also been running with a KASSERT since r222488 to make sure the
ipi_count is 0 on destroy.

PR: 164763
Reviewed by: gnn
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D5735