Add Port Scan Module

[Zamanry]

We need to add a port scan module that can be used to discover open SNMP ports. This would allow SNMPede to discover, spray, bulkwalk, and write SNMP once fully implemented rather than having to use other tools.

Please note that I've started this code, but was unable to get it working when testing demo.pysnmp.com:161/162. Although we can detect this open port with public community string, what if we didn't know it?