The insmntque() function associates a vnode with a mount. This includes updating v_mount for the vnode,
and inserting the vnode into the mount's vnode list.
The mount reference count is incremented for each vnode added to the mount, and that reference is
decremented by vgone(9).
The mount's interlock is held while the vnode is inserted. For MP-safe file systems, the vnode must be
exclusively locked.
On failure, insmntque() calls vgone(9) on the supplied vnode, and then drops the vnode lock and
reference. If more elaborated cleanup after insmntque() failure is needed, the insmntque1() function may
be used instead. The dtr argument is a pointer to a function that is called on failure. This function
may perform any custom cleanup. The vnode pointer is supplied as the first argument to dtr. The dtr_arg
argument is the second, supplying any additional context needed.