Conan O'Brien Challenges Conor To MMA Fight, McGregor Accepts!!

9:40 AM PT -- CoCo's in trouble ... 'cause Conor's taken notice, saying he's totally down for a fight ... and even threw Mark Wahlberg into the mix as well!!! "Challenge accepted Conan!" Conor tweeted. "I'll whoop you and Walhberg (sic) in the same…