net: atlantic: better loopback mode handling

net: atlantic: better loopback mode handling

commit b42726fcf76e9367e524392e0ead7e672cc0791c upstream.

Add checks to not enable multiple loopback modes simultaneously,
It was also discovered that for dma loopback to function correctly
promisc mode should be enabled on device.

Fixes: ea4b4d7fc106 ("net: atlantic: loopback tests via private flags")
Signed-off-by: Nikita Danilov <ndanilov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Dmitry Bogdanov <dbogdanov@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>