batman-adv: clarify CFG80211 dependency

The driver calls cfg80211_get_station, which may be part of a
module, so we must not enable BATMAN_ADV_BATMAN_V if
BATMAN_ADV=y and CFG80211=m:

net/built-in.o: In function `batadv_v_elp_get_throughput':
(text+0x5c62c): undefined reference to `cfg80211_get_station'

This clarifies the dependency to cover all combinations.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: c833484e ("batman-adv: ELP - compute the metric based on the estimated throughput")
Acked-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/batman-adv/Kconfig

@@ -17,7 +17,7 @@ config BATMAN_ADV
 
 config BATMAN_ADV_BATMAN_V
 	bool "B.A.T.M.A.N. V protocol (experimental)"
-	depends on BATMAN_ADV && CFG80211
+	depends on BATMAN_ADV && CFG80211=y || (CFG80211=m && BATMAN_ADV=m)
 	default n
 	help
 	  This option enables the B.A.T.M.A.N. V protocol, the successor