Cancels async port notifications on an object.
#include <zircon/syscalls.h> zx_status_t zx_port_cancel(zx_handle_t handle, zx_handle_t source, uint64_t key);
zx_port_cancel() is a non-blocking syscall which cancels
zx_object_wait_async() calls done with source and key.
When this call succeeds no new packets from the object pointed by source with key will be delivered to handle, and pending queued packets that match source and key are removed from the port.
handle must be of type ZX_OBJ_TYPE_PORT and have ZX_RIGHT_WRITE.
zx_port_cancel() returns ZX_OK if cancellation succeeded and
either queued packets were removed or pending
ZX_ERR_BAD_HANDLE source or handle is not a valid handle.
ZX_ERR_WRONG_TYPE handle is not a port handle.
ZX_ERR_ACCESS_DENIED source or handle does not have ZX_RIGHT_WRITE.
ZX_ERR_NOT_SUPPORTED source is a handle that cannot be waited on.
ZX_ERR_NOT_FOUND if either no pending packets or pending
zx_object_wait_async() calls with source and key were found.