NetworkPkg: Change the default IPv6 config policy

NetworkPkg: Change the default IPv6 config policy

The default policy for Ip6Config is Ip6ConfigPolicyAutomatic,
which results in all NIC ports starting SARR process when it
receives RA message with M flag from IPv6 router. So, this
patch is used to changes the the default IPv6 config policy to
Ip6ConfigPolicyManualand also defer the SetData operation after
Ip6ConfigProtocol installed. This update let the other platform
drivers have chance to change the default config data by consume
Ip6ConfigProtocol.

Cc: Subramanian Sriram <sriram-s@hpe.com>
Cc: El-Haj-Mahmoud Samer <samer.el-haj-mahmoud@hpe.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Subramanian Sriram <sriram-s@hpe.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>