By Tzvi Machlin The Carolina Panthers are already running four deep in the quarterback room heading into training camp. But it looks like they’re interested in bringing one more into the fold. According to NFL insider Bobby Thompson, the Panthers “still have interest” in signing a veteran quarterback. The Panthers started the offseason with Sam Darnold and P.J. Walker under contract. At the NFL Draft, the Panthers added a little more competition by taking Ole Miss gunslinger Matt Corral in the third round. They later signed Elon quarterback Davis Cheek as an undrafted free agent. But while the…