NetworkPkg/Ip6Dxe: Clean the invalid IPv6 configuration during driver start.

NetworkPkg/Ip6Dxe: Clean the invalid IPv6 configuration during driver start.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1448

*v3: Change the if condition check to only clean the invalid configuration.

*v2: Add the warning debug message.

This patch is to clean the invalid data and continue to start IP6 driver.

Cc: Michael Turner <Michael.Turner@microsoft.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>