core: error fix: right bound of range interval should be inclusive.

number of macs in range was invalid, missing one mac, which causes
system complaining about no available mac, when
same start mac and end mac was used. This is not ok, since validations
allows use of same start mac and end mac for given mac range.

Change-Id: I7f1257e752680b56decd69eb9a79caad97378e12
Bug-Url: https://bugzilla.redhat.com/1127245
Signed-off-by: Martin Mucha <mmucha@redhat.com>