MrsRyanGosling15
Oh God, how appalling for your friend's husband. Poor guy.
DollyPlastic,
Russell Sprout 
OP, Louis is a lovely name for boys. Classy and international. Absolutely stay with it for your little chap.
Don't worry at all; perhaps a few people might gently smile on hearing "Louis Walsh", but it wouldn't be anything more than recognition of someone in the public eye (and X Factor Louis is generally such a mild character; certainly no negative or dubious connotations etc. with the name).
As PPs have mentioned, the age disparity means that by the time your Louis and peers will be in any way aware of others' reactions, the popularity of Showbiz LW will be on the wane. It'll be a non-issue.
Meantime, you could always keep a snappy one-liner up your sleeve for any 'comedian' attempting a jibe...
Eejit:
"Louis Walsh? What, as in THE Louis Walsh off X Factor? Ha Ha, that's so funny!!!...."
You:
"Yeah, I hate name-dropping but he's actually DS's Great Uncle. So we promised to name him in his honour. But, please, please, keep it to yourself...I'd hate it to become common knowledge".