O Hostapd não lida com endereços IP, mas você pode restringir os ids da sua estação.
# Station MAC address -based authentication
# Please note that this kind of access control requires a driver that uses
# hostapd to take care of management frame processing and as such, this can be
# used with driver=hostap or driver=nl80211, but not with driver=madwifi.
# 0 = accept unless in deny list
# 1 = deny unless in accept list
# 2 = use external RADIUS server (accept/deny lists are searched first)
macaddr_acl=1
# Accept/deny lists are read from separate files (containing list of
# MAC addresses, one per line). Use absolute path name to make sure that the
# files can be read on SIGHUP configuration reloads.
accept_mac_file=/etc/hostapd/hostapd.accept
# deny_mac_file=/etc/hostapd/hostapd.deny
Normalmente, hostapd.accept
é suficiente para restringir o acesso.