batman-adv: Distributed ARP Table - create DHT helper functions

Add all the relevant functions in order to manage a Distributed Hash Table over
the B.A.T.M.A.N.-adv network. It will later be used to store several ARP entries
and implement DAT (Distributed ARP Table)

Signed-off-by: Antonio Quartulli <ordex@autistici.org>

net/batman-adv/main.h

@@ -73,6 +73,9 @@
 
 #define BATADV_LOG_BUF_LEN 8192	  /* has to be a power of 2 */
 
+/* numbers of originator to contact for any PUT/GET DHT operation */
+#define BATADV_DAT_CANDIDATES_NUM 3
+
 #define BATADV_VIS_INTERVAL 5000	/* 5 seconds */
 
 /* how much worse secondary interfaces may be to be considered as bonding
@@ -117,6 +120,9 @@ enum batadv_uev_type {
 
 #define BATADV_GW_THRESHOLD	50
 
+#define BATADV_DAT_CANDIDATE_NOT_FOUND	0
+#define BATADV_DAT_CANDIDATE_ORIG	1
+
 /* Debug Messages */
 #ifdef pr_fmt
 #undef pr_fmt