Solaris: shutdown in freevfs, not unmount

Solaris: shutdown in freevfs, not unmount

Call the afs shutdown sequence (afs_shutdown()) in the VFS_FREEVFS
handler, instead of in the VFS_UNMOUNT handler. This way we shutdown
when the last reference to our vfs goes away, instead of when we are
unmounted. That doesn't make much of a difference right now, but doing
so will be required for supporting forced unmounts.

Change-Id: I4158865b139d05e2955e4809b93628df27b83922
Reviewed-on: http://gerrit.openafs.org/1899
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>