Include 'extraTag' val in P4::Spec
The tagged output of a stream spec includes an 'extraTag<n>' field.
This change ensures that the field pointed to by 'extraTag' (such as
'firmerThanParent') is added to the P4::Spec object and it points
to the correct value.
Test case updated to check for 'firmerThanParent' in stream P4::Spec.
The test case needs to disconnect/connect, otherwise P4.run_streams
returns with the warning 'No such streams'.