MdeModulePkg: Fix default router table and interface missing error

MdeModulePkg: Fix default router table and interface missing error

Ip4StartAutoConfig() will always free its default router table and interface,
which may cause IP instance missing its correct default interface. e.g. when
the policy is dhcp, and one child is configured to use default address.

Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviwed-by: Ye Ting <ting.ye@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18245 6f19259b-4bc3-4df7-8a09-765794883524