net: hns3: use macro IANA_VXLAN_GPE_UDP_PORT to replace number 4790

This patch uses macro IANA_VXLAN_GPE_UDP_PORT to replace number 4790 for
cleanup.

Signed-off-by: Hao Chen <chenhao288@hisilicon.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>