Update component/coap to libcoap version release-4.2.0

This takes the code up to the latest released version of libcoap.

As there have been API changes, coap_client and coap_server in
examples/protocols have been updated to use the new APIs.

Further information on the new libcoap APIs can be found at
https://libcoap.net/doc/reference/4.2.0/

coap_client has been updated to handle BLOCK2 responses from
"coap://californium.eclipse.org"
coap_client has been modified to only send out one request (and wait for
the response)

coap_server has been updated to support Observe subscriptions, and well as
adding in PUT and DELETE handlers to work on the Espressif resource

coap_server and coap_client have had their stack sizes increased.

port/coap_io.c has been added, a copy of libcoap/src/coap_io.c with support
added for systems that do not have RFC 3542 section 20 support.

port/coap_io_socket.c has been removed as a lot of the code is now
replicated in different libcoap files.

Once this PR is place, then adding in DTLS will be a lot simpler (as a
separate PR)

Signed-off-by: Jitin George <jitin@espressif.com>

Merges https://github.com/espressif/esp-idf/pull/3148

components/coap/port/include/coap_config_posix.h

@@ -25,6 +25,7 @@
 #define HAVE_SYS_SOCKET_H
 #define HAVE_MALLOC
 #define HAVE_ARPA_INET_H
+#define HAVE_TIME_H
 
 #define IP_PKTINFO   IP_MULTICAST_IF
 #define IPV6_PKTINFO IPV6_V6ONLY
@@ -32,10 +33,7 @@
 #define PACKAGE_NAME "libcoap-posix"
 #define PACKAGE_VERSION "?"
 
-#define CUSTOM_COAP_NETWORK_ENDPOINT
-#define CUSTOM_COAP_NETWORK_SEND
-#define CUSTOM_COAP_NETWORK_READ
-
-#endif
+#define COAP_BAD_RECVMSG
 
+#endif /* WITH_POSIX */
 #endif /* COAP_CONFIG_POSIX_H_ */