1. Fix a bug in Dhcp4 to prevent unexpected broadcast DHCP packets be queued up in...

1. Fix a bug in Dhcp4 to prevent unexpected broadcast DHCP packets be queued up in the system: these packets will never be freed and will cumulate as time goes on, and then it will cause the system becomes very slow. This issue is reported by HP.
2. Sync HSD #210249 patch: Fix bug in handling certain network errors in EfiDhcp4TransmitReceive() for DHCP4 driver
3. Enhance DhcpCleanLease to clear Netmask as well, so that Dhcp4->GetModeData() could return clean data in Dhcp4Stopped state.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9354 6f19259b-4bc3-4df7-8a09-765794883524