hostapd.sh: Add support for "anonymous_identity" config field

The wpa_supplicant supports an "anonymous_identity" field, which some
EAP networks require.  From the documentation:

anonymous_identity: Anonymous identity string for EAP (to be used as the
    unencrypted identity with EAP types that support different tunnelled
    identity, e.g., EAP-TTLS).

This change modifies the hostapd.sh script to propagate this field
from the UCI config to the wpa_supplicant.conf file.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Reviewed-by: Manuel Munz <freifunk@somakoma.de>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 49181