Merge branch 'net-dev-Make-protocol-ptr-dependent-on-CONFIG'

David Ahern says:

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net: dev: Make protocol ptr dependent on CONFIG

Found these in a branch from 3-years ago. Still relevant today.
Make decnet, ax25, and atalk ptrs in net_device based on their
respective CONFIG.
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Signed-off-by: David S. Miller <davem@davemloft.net>