MdeModulePkg: Support classless IP for DHCPv4 TransmitReceive()

MdeModulePkg: Support classless IP for DHCPv4 TransmitReceive()

The IP address should not be treated as classful one if DHCP options
contain a classless IP with its true subnet mask. Otherwise, DHCPv4
TransmitReceive() will failed. This real subnet mask will be parsed
and recorded in DhcpSb->Netmask. So, we need check it before get the
IP's corresponding subnet mask.

Cc: Santhapur Naveen <naveens@amiindia.co.in>
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: Fu Siyuan <siyuan.fu@intel.com>