sample: net: wifi: reduce timeout for ICMP probe sent by server

DHCPv4 server will probe the offered IP address (send ICMP echo request)
and wait for 1s (default) before offering the address. STA sends out DHCP
discover, but gets no response. Windows automatically assigns the network
card an IP address of 169.254.xx.xx.
So set timeout for ICMP probe sent by the server to 100ms.

Signed-off-by: Gang Li <gang.li_1@nxp.com>