Release the vnode lock and close the linker file vnode earlier in

Release the vnode lock and close the linker file vnode earlier in
the linker_load_file methods. The change is that the consequent
linker_file_unload() call is not under the vnode lock anymore.
This prevents the LOR between kernel linker sx xlock and vnode lock,
because linker_file_unload() relocks kernel linker lock.

MFC after:	2 weeks