Take a look at this link http://manpages.ubuntu.com/manpages/intrepid/man5/udhcpd.conf.5.html it will show you the proper way and multiple options of configuring udhcpd. Also, take a look at this examples http://git.busybox.net/busybox/tree/examples/udhcp/udhcpd.conf . The error you are getting “ address already in use” might be because while setting the dns and dhcp addresses, you might have them configured to overlap each other. Make sure the dns addresses range is separate from the dhcp addresses.
might be of interest:The Intel IoT Devkit SD card image uses a pretty recent connman. However, haven't tried udhcpd as connman provides dhcp (not sure what it actually uses).
The image also comes with avahi. But it's not compatible with AlexT_Intel 's image
Thanks for your reply, that put me on the right track. By digging a little bit more I have found THE tutorial to setup my hotspot: RPI-Wireless-Hotspot - eLinux.org
I just followed the instruction and it worked perfectly ! I have been able to connect several client device on my hotspot without any issue.
I definitely recommend that tutorial for everyone who want to set a DHCP server.
Thank you all,