fix minor bugs related with dhcp

	- get_free_ip_from_range() was calculating wrong the free ip for if first and last ip is given and the range is lower than the CIDR
	- Namespace loopback up must be forced.
	- is_dhcp_port_free() mysql query fix

Change-Id: I1bbf9ed2c23945accc16c75d4e75da4b62ce745c
Signed-off-by: mirabal <leonardo.mirabal@altran.com>