net: Revert "tftp: adjust settings to be suitable for 100Mbit ethernet"

Commit 620776d7 "tftp: adjust settings to be suitable for 100Mbit ethernet"
causes the following error message when trying to load a file using 'tftp'
command via a tftp server.

    TFTP error: 'Unsupported option(s) requested' (8)

This is due to with commit 620776d7 changes, the tftp option 'timeout'
value is now set to zero which is an invalid value as per RFC2349 [1].
Valid values range between "1" and "255" seconds, inclusive. With some
tftp servers that strictly implement the RFC requirement, it reports
such an error message.

Revert commit 620776d7 for RFC compliance.

[1] https://www.ietf.org/rfc/rfc2349.txt



Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>