ping tests: Fix test on i386 platforms

Actually use INT_MAX (0x7fffffff), not UINT_MAX (0xffffffff) to avoid
overflowing time_t and missing the test.

Reported by:	Jenkins
Reviewed by:	markj
Fixes:		5b8af90 ("ping: Add ATF-Python tests")
Pull Request:	freebsd/freebsd-src#874
Differential Revision: https://reviews.freebsd.org/D42268

sbin/ping/tests/test_ping.py

@@ -51,7 +51,7 @@ def build_response_packet(echo, ip, icmp, oip_ihl, special):
         # Build a package with a timestamp of INT_MAX
         # (time-warped package)
         payload_no_timestamp = sc.bytes_hex(load)[16:]
-        load = (b"\xff" * 8) + sc.hex_bytes(payload_no_timestamp)
+        load = b"\x7f" + (b"\xff" * 7) + sc.hex_bytes(payload_no_timestamp)
     if special == "wrong":
         # Build a package with a wrong last byte
         payload_no_last_byte = sc.bytes_hex(load)[:-2]