brcm63xx: mac80211.sh: use DFS workaround for AP

Use DFS workaround only for AP interface.
In other case we hit strange problem:
 - have wlX as a station
 - have wlX.1 as a AP

Hostapd startup failed on wlX.1 while
macaddr set IOCTL fail.

Interesting that we/hostapd can change/set mac
address only when wl is down.

root@iopsys:~# ifconfig wl2.1 hw ether EE:6C:9A:52:AC:CB
ifconfig: SIOCSIFHWADDR: I/O error
root@iopsys:~# wl -i wl1 isup
1
root@iopsys:~#

Signed-off-by: Janusz Dziedzic <janusz.dziedzic@iopsys.eu>