FreeBSD: Return ifndef IN_BASE back to fix the build

[amotin]

FreeBSD's libprocstat seems to build kernel code in user space, which does not work here due to undefined vnode_t. It's a mess.

While there, remove some unused illumos compat from vnode.h.

How Has This Been Tested?

Run FreeBSD world+kernel build with this change in.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[amotin]

@mmatuska ^^^

[mmatuska]

@mmatuska ^^^

@amotin builds fine on base, thanks!