MdeModulePkg: Remove TransmitReceive() and ActiveChild dependency

MdeModulePkg: Remove TransmitReceive() and ActiveChild dependency

Fix git 59a8cfd4 (SVN r17869) removes DHCP4.TransmitReceive()and DORA
process dependency, but it updated TransmitReceive() to take the ownership
of DhcpSb->ActiveChild but never release it. This will break the retransmit
and lease time out counter of DORA.
To fix that, TransmitReceive() doesn't need to be the ActiveChild, and the
timer routine should be updated to handle the TransmitReceive specially.

Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18048 6f19259b-4bc3-4df7-8a09-765794883524