toolchain/uClibc: enable UCLIBC_SUPPORT_AI_ADDRCONFIG

Enable AI_ADDRCONFIG support in uClibc otherwise we don't get the
ifaddrs.h header installed and thus lack getifaddrs support.
Quite useful for samba for example so we can use interfaces=eth0 statements in
the configuration file rather than klunkier
interfaces=192.168.1.1/255.255.255.0 ones.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>