batman-adv: enable DAT by default at compile time

DAT (Distributed ARP Table) has been enabled by default
in the out-of-tree batman-adv kernel module for several
years already.
It can now be enabled in the kernel too.
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/Kconfig

@@ -60,7 +60,7 @@ config BATMAN_ADV_BLA
 config BATMAN_ADV_DAT
 	bool "Distributed ARP Table"
 	depends on BATMAN_ADV && INET
-	default n
+	default y
 	help
 	  This option enables DAT (Distributed ARP Table), a DHT based
 	  mechanism that increases ARP reliability on sparse wireless