UDP ports --echo out properly

[githubparser]

masscan expects U:, not +0x10000. this patch makes the --echo output readable as input for UDP ports.

before:

$ masscan -p22,U:123,U:161-162 --echo | grep ports
ports = 22,65659,65697-65698

after:

masscan -p22,U:123 --echo | grep ports
ports = 22,U:123,U:161-162

[githubparser]

This evidently breaks paused.conf output for things like --script ntp-monlist, where it's not recording a typical port range value, so I'm not sure whether that needs to be changed, or this patch..