使用lwip调试tcpserver时，出现绑定端口失败，通过ifconfig发现是dhcp还未获取到ip导致的，等到ip获取成功之后就可以通过sal的bind进行绑定端口了。
msh >tcpserver
Bind fail!
close listener...
msh >tcpserver
Bind fail!
close listener...
msh >ifconfig
network interface device: e0 (Default)
MTU: 1500
MAC: 00 80 e1 12 26 2c
FLAGS: UP LINK_UP INTERNET_DOWN DHCP_ENABLE ETHARP BROADCAST IGMP
ip address: 0.0.0.0
gw address: 0.0.0.0
net mask : 0.0.0.0
dns server #0: 192.168.1.1
dns server #1: 0.0.0.0
msh >ifconfig
network interface device: e0 (Default)
MTU: 1500
MAC: 00 80 e1 12 26 2c
FLAGS: UP LINK_UP INTERNET_UP DHCP_ENABLE ETHARP BROADCAST IGMP
ip address: 192.168.1.42
gw address: 192.168.1.1
net mask : 255.255.255.0
dns server #0: 192.168.1.1
dns server #1: 0.0.0.0
msh >tcpserver
begin listing...
