hsr: remove WARN_ONCE() in hsr_fill_frame_info()

When VLAN frame is being sent, hsr calls WARN_ONCE() because hsr doesn't
support VLAN. But using WARN_ONCE() is overdoing.
Using netdev_warn_once() is enough.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>