net: wget: fix TCP sequence number wrap around issue

If tcp_seq_num is wrap around, tcp_seq_num >= initial_data_seq_num
isn't satisfied and store_block() isn't called.
The condition has a wrap around issue, so it is fixed in this patch.

Signed-off-by: Yasuharu Shibata <yasuharu.shibata@gmail.com>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Suggested-by: Michael Trimarchi <michael@amarulasolutions.com>
Reported-by: Tim Harvey <tharvey@gateworks.com>
Tested-by: Fabio Estevam <festevam@denx.de>