hostapd: use getrandom syscall

hostapd: use getrandom syscall

hostapd will not use the getrandom() syscall and as a fallback use
/dev/random, the syscall is supported since Linux 3.17 and in the musl,
glibc and uclibc version used by OpenWrt.

Signed-off-by: Hauke Mehrtens <[email protected]>
(cherry picked from commit 998686364da7d002ba9f6dbb43cc5f32294dd4ab)