vxlan: Move address helpers to private headers
Move the helpers out of the core C file to the private header so that
they could be used by the upcoming MDB code.
While at it, constify the second argument of vxlan_nla_get_addr().
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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