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.

Approved by: re (cperciva)
Sponsored by: The FreeBSD Foundation

(cherry picked from commit e93db9abc9a62d662c40d783663d64cdb829a0cc)
(cherry picked from commit 469ab88d107c05ab533a15d4014d1a97b5a13c86)