配置wifi的AP模式
配置wifi的AP模式：
需要busybox里面有ifconfig，udhcpd，tcpsvd，ftpd
另外有hostapd
加载wifi驱动时要设置op_mode为AP模式
作者的wifi模块是博通的，modprobe bcmdhd op_mode=2
ifconfig wlan0 up
hostapd -B /etc/hostapd.conf
udhcpd /etc/udhcpd.conf
tcpsvd 0 21 ftpd -w /data &
udhcpd.conf：
1 # The start and end of the IP lease block
2 start 192.168.1.2
3 end 192.168.1.255
4
5 # The interface that udhcpd will use
6 interface wlan0 hostapd.conf：
1 ssid=alvin
2 ctrl_interface=/var/run/hostapd
3 hw_mode=g
4 channel=1
5 interface=wlan0
6 driver=nl80211
7 ignore_broadcast_ssid=0
8 wpa=2
9 wpa_passphrase=12345678
10 wpa_key_mgmt=WPA-PSK
11 rsn_pairwise=CCMP