MFC r330387 and r330396:
Rename the SLAB_DESTROY_BY_RCU flag into SLAB_TYPESAFE_BY_RCU in the LinuxKPI
to be compatible with Linux.

Keep the old SLAB_DESTROY_BY_RCU macro definition around in the LinuxKPI
to avoid compilation breakage in external kernel modules.

Requested by: Johannes Lundberg <johalun0@gmail.com>
Sponsored by: Mellanox Technologies