CLEANUP: Fix typos in the dns subsystem

Fix misspells in the code comments of the dns subsystem.
diff --git a/include/types/dns.h b/include/types/dns.h
index 488d399..d7afe02 100644
--- a/include/types/dns.h
+++ b/include/types/dns.h
@@ -88,7 +88,7 @@
 #define DNS_FLAG_TRUNCATED      0x0200  /* mask for truncated flag */
 #define DNS_FLAG_REPLYCODE      0x000F  /* mask for reply code */
 
-/* max number of network preference entries are avalaible from the
+/* max number of network preference entries are available from the
  * configuration file.
  */
 #define SRV_MAX_PREF_NET 5
@@ -244,7 +244,7 @@
 			struct in6_addr in6;
 		} mask;
 	} pref_net[SRV_MAX_PREF_NET];
-	int pref_net_nb; /* The number of registered prefered networks. */
+	int pref_net_nb; /* The number of registered preferred networks. */
 	int accept_duplicate_ip; /* flag to indicate whether the associated object can use an IP address
 				    already set to an other object of the same group */
 };
@@ -265,7 +265,7 @@
 	unsigned int          last_valid;          /* time of the last valid response */
 	int                   query_id;            /* DNS query ID dedicated for this resolution */
 	struct eb32_node      qid;                 /* ebtree query id */
-	int                   prefered_query_type; /* prefered query type */
+	int                   prefered_query_type; /* preferred query type */
 	int                   query_type;          /* current query type  */
 	int                   status;              /* status of the resolution being processed RSLV_STATUS_* */
 	int                   step;                /* RSLV_STEP_* */
@@ -292,7 +292,7 @@
 
 /* Last resolution status code */
 enum {
-	RSLV_STATUS_NONE = 0,  /* no resolution occured yet */
+	RSLV_STATUS_NONE = 0,  /* no resolution occurred yet */
 	RSLV_STATUS_VALID,     /* no error */
 	RSLV_STATUS_INVALID,   /* invalid responses */
 	RSLV_STATUS_ERROR,     /* error */
diff --git a/src/dns.c b/src/dns.c
index 57bec21..5bce18b 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -974,14 +974,14 @@
 	max_score         = -1;
 
 	/* Select an IP regarding configuration preference.
-	 * Top priority is the prefered network ip version,
-	 * second priority is the prefered network.
+	 * Top priority is the preferred network ip version,
+	 * second priority is the preferred network.
 	 * the last priority is the currently used IP,
 	 *
 	 * For these three priorities, a score is calculated. The
 	 * weight are:
-	 *  8 - prefered ip version.
-	 *  4 - prefered network.
+	 *  8 - preferred ip version.
+	 *  4 - preferred network.
 	 *  2 - if the ip in the record is not affected to any other server in the same backend (duplication)
 	 *  1 - current ip.
 	 * The result with the biggest score is returned.
@@ -1003,11 +1003,11 @@
 			continue;
 		score = 0;
 
-		/* Check for prefered ip protocol. */
+		/* Check for preferred ip protocol. */
 		if (ip_type == family_priority)
 			score += 8;
 
-		/* Check for prefered network. */
+		/* Check for preferred network. */
 		for (j = 0; j < dns_opts->pref_net_nb; j++) {
 
 			/* Compare only the same adresses class. */