The Chargers have three players who received a game designation ahead of Sunday’s Week 4 game against the Texans. COSTA MESA – The Chargers will enter Sunday’s contest against the Texans with wide receiver Keenan Allen ruled out, and center Corey Linsley and tight end Donald Parham Jr. considered questionable. Allen felt some discomfort in his hamstring on Thursday, so he won’t play this weekend. As for Linsley, coach Brandon Staley said his expectations are for him to be the starting center this week. Staley also said they’ll probably lean on the side of caution with Parham, holding him out…