dnsmasq: bump to version 2.75

[Thomas: applying for 2015.08, because it fixes a regression
introduced in dnsmasq 2.74, as reported by Gustavo.]

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>