octeontx2-pf: Dont enable backpressure on LBK links

Avoid configure backpressure for LBK links as they
don't support it and enable lmacs before configuration
pause frames.

Fixes: 75f36270 ("octeontx2-pf: Support to enable/disable pause frames via ethtool")
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>