There is a ???? in ????? – I cannot remember exactly where – which speaks about davening in shorts [which was definitely not the accepted thing in those days], yet the only problem defined is ???? ?????, that a guy in shorts cannot be ?”?. It sounds like just davening in shorts is not even a problem..
[DISCLAIMER: I MEAN NOT TO PASKEN, SPEAK TO YOUR LOR. PERSONALLY, I WOULD NEVER DAVEN IN SHORTS. I AM JUST POINTING OUT THAT MAY BE HALACHICALLY PERMITED