octeontx2-pf: Clear RSS enable flag on interace down

RSS configuration can not be get/set when interface is in down state
as they required mbox communication. RSS enable flag status
is used for set/get configuration. Current code do not clear the
RSS enable flag on interface down which lead to mbox error while
trying to set/get RSS configuration.

Fixes: 85069e95 ("octeontx2-pf: Receive side scaling support")
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>