hostapd: use internal crypto library

When OpenSSL is not enabled, hostapd relies on an internal
library. However, this library must be enabled, otherwise the
compilation of hostapd fails with:

/home/test/ctng-arm-eglibc/bin/../lib/gcc/arm-unknown-linux-gnueabi/4.3.4/../../../../arm-unknown-linux-gnueabi/bin/ld: cannot find -ltommath

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>