cam: Bump deprecated sysctl removal to 16

The descriptions for these unmapped_io and rotating sysctls indicated
that they're deprecated and being removed for FreeBSD 15.0. That did
not happen, so update to FreeBSD 16 instead.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit e93db9abc9a62d662c40d783663d64cdb829a0cc)