NetworkPkg: Source fixes and cleanup for ARMGCC compiles

NetworkPkg: Source fixes and cleanup for ARMGCC compiles

- Fix EFI_IPv4_ADDRESS usages to use a macro to copy the structure
   instead of direct assignment, to avoid runtime alignment errors.
- Delete excess local variables that are initialized but otherwise unused.
- Add LibraryClasses.ARM & AARCH64 section in NetworkPkg.dsc file,
   containing a CompilerIntrinsicsLib null-library, required for successful
  standalone package builds (copied from MdeModulePkg.dsc).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Randy Pawell <randy_pawell@hp.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16472 6f19259b-4bc3-4df7-8a09-765794883524