netd: add support for legacy hostapd

Implements BOARD_HAVE_LEGACY_HOSTAPD, to avoid passing
"ieee80211n=1" to hostapd config.

Change-Id: I7d77c83f8583cb7c577d43081fef3f09e7cd077d
netd: workaround to skip wifi fw reload

Implements BOARD_WLAN_NO_FWRELOAD, needed for some drivers that
do not support firmware reload (such as ar6000/ath6kl).

Change-Id: I20628798c2528636068dee9d0611bc440330dd85