Street smarts is when you are able to go about whatever business you need to go about on the streets, but playin it clever so you dont end up in a situation to get yourself in trouble.
For example, if, say 5-0 are on your case or somethin, and you're able to keep one step ahead of them with a smart game plan, that could be considered to be possessin street smarts.
Ghetto mentality is when you're in a state of mind as if to say, "fuck it, i gotta get by, by any means possible, and no one ain't gonna get in my way..."
So that means that if you gotta kill, sell hard drugs, jack people etc. in order to get on with your life, you won't think twice about doin it cos in your opinion it needs to be done, whereas someone with street smarts will find an alternative method of dealing with things.