tcp-socket: Do not move extra data once acknowledged

By design, s->output_data_send_nxt can not be larger than s->output_data_len.
Hence, the corresponding test is useless, and only the remaining data passed to
tcp_socket_send() has to be moved to the beginning of the output buffer after
acknowledgement instead of the whole buffer remainder.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
http-socket: Use puts() instead of printf() for simple strings

puts() is more efficient than printf() for simple strings, both because the
string has not to be parsed during printing, and because the terminating new
line character has not to be stored. Hence, use puts() by default. This also
fixes the missing new line character for the "null url" and "empty url"
messages.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
http-socket: Fix HTTP_SOCKET_OUTPUTBUFSIZE

The return values of the calls to tcp_socket_send_str() are ignored, so, in
order to keep things simple, HTTP_SOCKET_OUTPUTBUFSIZE has to be large enough to
contain the longest possible request, which is 143 characters with the current
code. Round this value up to 256 to keep room for future enhancements.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
http-socket: Add callback event to report header information

Replace the HTTP_SOCKET_404 event with a HTTP_SOCKET_HEADER event reporting more
useful information to the callback. As of now, the status code and the content
length are passed with this event.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
http-socket: Add support for partial GET

This requires switching to HTTP/1.1, so non-persistent connections are requested
in order not to change the client-side behavior.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
http-socket: Add support for POST

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Update contiki

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>