Changes

tests/cnpool.vty: Skip non-related fields under cs7 instance

libosmo-sigtran now always prints network-indicator, which creates an
unexpected output during cnpool.vty test.
Make sure it doesn't interfere with what we are really testing there.

Related: libosmo-sigtran.git a11b2bfff289b09f4c9e964b763df288ace8304a

Change-Id: I0e53cacbb0004f91c67f4c0bcb9b1d041fb534dd