Introduce ipa_endpoint_status_tag(), which returns true if received
status indicates its tag field is valid.  The endpoint parameter is
not yet used.

Call this from ipa_status_drop_packet(), and drop the packet if the
status indicates the tag was valid.  Pass the endpoint pointer to
ipa_status_drop_packet(), and rename it ipa_endpoint_status_drop().
The endpoint will be used in the next patch.
Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>