tcp: tweak tcp_sock_write_txrx size assertion

I forgot 32bit arches might have 64bit alignment for u64
fields.

tcp_sock_write_txrx group does not contain pointers,
but two u64 fields. It is possible that on 32bit kernel,
a 32bit hole is before tp->tcp_clock_cache.

I will try to remember a group can be bigger on 32bit
kernels in the future.

With help from Vladimir Oltean.

Fixes: d2c3a7eb ("tcp: more struct tcp_sock adjustments")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404082207.HCEdQhUO-lkp@intel.com/Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20240409140914.4105429-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp.c

@@ -4673,7 +4673,11 @@ static void __init tcp_struct_check(void)
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, app_limited);
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rcv_wnd);
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rx_opt);
-	CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 92);
+
+	/* 32bit arches with 8byte alignment on u64 fields might need padding
+	 * before tcp_clock_cache.
+	 */
+	CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 92 + 4);
 
 	/* RX read-write hotpath cache lines */
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_rx, bytes_received);