net: hns: Remove unused function declaration mac_adjust_link()

Commit 511e6bc0 ("net: add Hisilicon Network Subsystem DSAF support")
declared but never implemented this, remove it.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Hao Lan <lanhao@huawei.com>
Link: https://lore.kernel.org/r/20230804130048.39808-1-yuehaibing@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>