UDP scan RPORT option update

MSP-11652

This option was added at https://github.com/rapid7/metasploit-framework/pull/4113/files#diff-e9ac58cf40e1afdd1aecf8742cf6aaa6R24 Its addition caused Pro Discover scan to never run UDP scan and instead showed:
```
 ( UDP ) error: Msf::OptionValidateError The following options failed to validate: RPORT.
```

## msfconsole
- [x] ```use auxiliary/scanner/discovery/udp_sweep```
- [x] ```set RHOSTS xxxx```
- [x] ```run```
- [x] Verify you get UDP service discovery info back, no RPORT error

## Pro Discover
- [x] See Jira ticket for steps