net: hns3: add Asym Pause support to fix autoneg problem

Local device and link partner config auto-negotiation on both,
local device config pause frame use as: rx on/tx off,
link partner config pause frame use as: rx off/tx on.

We except the result is:
Local device:
Autonegotiate:  on
RX:             on
TX:             off
RX negotiated:  on
TX negotiated:  off

Link partner:
Autonegotiate:  on
RX:             off
TX:             on
RX negotiated:  off
TX negotiated:  on

But actually, the result of Local device and link partner is both:
Autonegotiate:  on
RX:             off
TX:             off
RX negotiated:  off
TX negotiated:  off

The root cause is that the supported flag is has only Pause,
reference to the function genphy_config_advert():
static int genphy_config_advert(struct phy_device *phydev)
{
	...
	linkmode_and(phydev->advertising, phydev->advertising,
		     phydev->supported);
	...
}
The pause frame use of link partner is rx off/tx on, so its
advertising only set the bit Asym_Pause, and the supported is
only set the bit Pause, so the result of linkmode_and(), is
rx off/tx off.

This patch adds Asym_Pause to the supported flag to fix it.

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>