fixed internally Mission 4 incorrect radio freq

[TLTeo]

During Mission 4 I had to divert to Al Dhafra because after Weed refueled, the S-3 did a DCS AI and literally decided to fly straight vertical up to 1000 KIAS up to angels 250, and in the meantime I was down to ~1.5k lbs of gas. It was a thing of beauty. Anyway, Red 2 is tuned to 250.9, which should be Al Dhafra ATC, but it's the wrong frequency. The correct one is 251.1. Once I tuned to it I could contact them and land just fine.

[baltic_dragon]

Thanks, updated!