OpenZFS changed the define _OPENSOLARIS_SYS_TYPES_H_ to
_SPL_SYS_TYPES_H_ to guade the sys/types.h compatibility stuff. Follow
the change here. The only place in the tree _OPENSOLARIS_SYS_TYPES_H_ is
mentioned is in the /* _OPENSOLARIS_SYS_TYPES_H_ */ at the end of
sys/types.h. That needs to be changed upstream in OpenZFS since we don't
like changing things in FreeBSD's tree.

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