Bug 2460 - Converting ipv4 to ipv4Prefix requires mask

Starting on fixes for Bug 1953, the validation of IPv4Prefix
will make sure mask is being provided.

Patch Set 2: Move the +"/32" to a common utility function.

Ref gerrit: https://git.opendaylight.org/gerrit/#/c/11384/

Change-Id: I84771d087d7ed1ec5cc8045e3efe3673e6969d5c
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>