mem-ruby: missing method in NetDest interface

Change-Id: Ibf651c37c50174186daebebc06aa115e6bc2ed33
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31262
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Bradford Beckmann <bradford.beckmann@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/ruby/protocol/RubySlicc_Types.sm

@@ -111,6 +111,7 @@ structure (NetDest, external = "yes", non_obj="yes") {
   bool isEmpty();
   bool intersectionIsEmpty(Set);
   bool intersectionIsEmpty(NetDest);
+  MachineID smallestElement();
   MachineID smallestElement(MachineType);
   NetDest OR(NetDest);
   NetDest AND(NetDest);