aliyun: reuse ipv4 gateway address returned by metadata server
The default ipv4 gateway address of the VPC in Aliyun cloud is not the
first IP address in the CIDR subnet block, we should instead use the
ipv4 gateway address retrieved from the metadata server in
_nmc_mangle_connection()
.
Signed-off-by: Wen Liang liangwen12year@gmail.com