As far as we know, Damage Control is still stuck in developmental limbo. No word on it has come out since it failed to make the 2016 pilot season last year, and it also missed again this year. It is increasingly looking like the show's not going to happen.
There has not been any official cancellation announcement from ABC. The last official statement I can find from anyone involved is from ABC president Paul Lee, from last year, claiming that Damage Control was ready to go:
That’s the one that’s going to be coming out this season. I haven’t read it yet. I can’t wait to see it. We hope it’s going to be great.
Obviously, that didn't happen. The other Marvel TV show that was in production at the same time as Damage Control (Most Wanted, based on the then-recently-fired SHIELD agents Bobbi and Hunter) was also never picked up to series, though that one was explicitly "rejected".
Since then, both Inhumans and Cloak and Dagger have been pushed to series (Inhumans likely as a replacement for the aging Agents of SHIELD which is expected not to get another season in the 2018-2019 schedule.) If ABC wanted to push Damage Control to production, it seems like they had a perfect chance and didn't take it.
So, no, the mention of Damage Control in the Spider-Man: Homecoming movie is not an official back-door pilot. It's very possible that it's an attempt by Marvel to drum up support for it to move forward, but given the ABC TV landscape, I'm not holding my breath.