net: hsr: define and use proto_ops ptrs to handle hsr specific frames

As a preparatory patch to introduce PRP, refactor the code specific to
handling HSR frames into separate functions and call them through
proto_ops function pointers.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>