mlxsw: spectrum: Prevent overwrite of DCB capability fields

The number of supported traffic classes that can have ETS and PFC
simultaneously enabled is not subject to user configuration, so make
sure we always initialize them to the correct values following a set
operation.

Fixes: 8e8dfe9f ("mlxsw: spectrum: Add IEEE 802.1Qaz ETS support")
Fixes: d81a6bdb

 ("mlxsw: spectrum: Add IEEE 802.1Qbb PFC support")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>