Fix logic in adding prefix to ip-a in classifier

This commit has following changes:

- When 'source-ip-address' or 'destination-ip-address' are not provided
  under "nsd:nsd-catalog:nsd:vnffgd:classifier:match-attributes" this
  would avoid adding the '/32' prefix in the classifier definition.

- add details to classifier definition only if provided.

This patch helps us in creating classifier with minimum details and
avoid errors when 'source-ip-address' or  'destination-ip-address'
 were not provided in nsd.

Change-Id: I5b572552bd670b56faa0aba5833209d198e10450
Signed-off-by: Venkata Harshavardhan Reddy Allu <venkataharshavardhan_ven@srmuniv.edu.in>