Introduction of sequential-API build variant, better thread safety (lwIP only)

ext/picotcp/modules/pico_dns_client.h

@@ -37,9 +37,6 @@
 #define PICO_DNS_RR_A_RDLENGTH 4
 #define PICO_DNS_RR_AAAA_RDLENGTH 16
 
-#ifdef __cplusplus
-extern "C" {
-#endif
 int pico_dns_client_init(void);
 /* flag is PICO_DNS_NS_DEL or PICO_DNS_NS_ADD */
 int pico_dns_client_nameserver(struct pico_ip4 *ns, uint8_t flag);
@@ -49,8 +46,5 @@ int pico_dns_client_getname(const char *ip, void (*callback)(char *url, void *ar
 int pico_dns_client_getaddr6(const char *url, void (*callback)(char *, void *), void *arg);
 int pico_dns_client_getname6(const char *url, void (*callback)(char *, void *), void *arg);
 #endif
-#ifdef __cplusplus
-}
-#endif
 
 #endif /* _INCLUDE_PICO_DNS_CLIENT */