6loWPAN: Fix compile errors and warnings when building the complete 6loWPAN configuration.

libc/netdb/lib_dnscache.c

@@ -268,8 +268,8 @@ int dns_find_answer(FAR const char *hostname, FAR struct sockaddr *addr,
               /* We have a match.  Return the resolved host address */
 
 #ifdef CONFIG_NET_IPv4
-              if (entry->addr.addr.sa_family == AF_INET)
 #ifdef CONFIG_NET_IPv6
+              if (entry->addr.addr.sa_family == AF_INET)
 #endif
                 {
                    inlen = sizeof(struct sockaddr_in);
@@ -277,8 +277,8 @@ int dns_find_answer(FAR const char *hostname, FAR struct sockaddr *addr,
 #endif
 
 #ifdef CONFIG_NET_IPv6
-              else
 #ifdef CONFIG_NET_IPv4
+              else
 #endif
                 {
                    inlen = sizeof(struct sockaddr_in6);

libc/netdb/lib_dnsinit.c

@@ -39,6 +39,7 @@
 
 #include <nuttx/config.h>
 
+#include <string.h>
 #include <semaphore.h>
 #include <errno.h>
 #include <assert.h>