mlxsw: spectrum_dcb: Rename mlxsw_sp_port_headroom_set()

mlxsw_sp_port_headroom_set() is defined twice - in spectrum.c and in
spectrum_dcb.c, with different arguments and different implementation
but the name is same.

Rename mlxsw_sp_port_headroom_set() to mlxsw_sp_port_headroom_ets_set()
in order to allow using the second function in several files, and not
only as static function in spectrum.c.

Signed-off-by: Amit Cohen <amitc@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>