By Tzvi Machlin The defending Super Bowl champion Los Angeles Rams retained a lot of their core players from last year’s title-winning team. But one linebacker is set for a potentially long layoff to start the campaign. According to NFL insider Ian Rapoport, Rams linebacker Travin Howard is set to undergo core muscle surgery from Dr. William Meyers. Howard had previously been placed on the physically unable to perform (PUP) list with a groin injury. The surgery is slated for early this week, which bodes well for Howard’s return timetable. Rapoport speculated that the timing of the surgery give…