linux(4): Handle cas failure on ll/sc operations

Follow the 11a6ecd4. Check and handle the case when the ll/sc casu fails
even when the compare succeeds.

For more details PR/263825, https://reviews.freebsd.org/D35150.

Obtained from:		Andrew@
MFC after:		2 weeks

sys/compat/linux/linux_futex.c

@@ -410,6 +410,17 @@ linux_futex_lock_pi(struct thread *td, bool try, struct linux_futex_args *args)
 			break;
 		}
 
+		/*
+		 * Nobody owns it, but the acquire failed. This can happen
+		 * with ll/sc atomic.
+		 */
+		if (owner == 0) {
+			error = thread_check_susp(td, true);
+			if (error != 0)
+				break;
+			continue;
+		}
+
 		/*
 		 * Avoid overwriting a possible error from sleep due
 		 * to the pending signal with suspension check result.