Returns a JSON array of all configured VLANs with their IDs and names,
e.g. [{"id":1,"name":""},{"id":20,"name":"IoT"}].
The endpoint iterates VLAN IDs 1..4094 and filters by the validity bit
in sfr_data[0] (0x02), following the same pattern as vlan_create() and
vlan_setup() in rtl837x_port.c.
Also adds a small itoa16_html() helper for emitting decimal numbers
up to 4 digits (analogous to the existing 8-bit itoa_html()), used
for VLAN IDs which can reach 4094. Response builder uses the existing
vlan_name() helper for the name lookup, consistent with send_vlan().
Buffer overflow is prevented by breaking out of the iteration loop at
TCP_OUTBUF_SIZE - 60.
This endpoint is the foundation for upcoming UI improvements
(VLAN selector dropdown and overview table).
With content_type = "application/x-www-form-urlencoded", "+" means space.
This case was not handled.
Also refactor the code to make a loop to process the hex digits.
Chrome sends upload requests using POST with multipart/form-data
content type in multiple packets for the header part of the form-data.
Introduce a TSTATE_MULTIPART for the httpd server states that denotes
that so far only a part of the multipart header has been transmitted.
Once the full header has been transmitted, we change to TSTATE_POST
as for Firefox which sends all the multipart header in one piece.
The main further change required then is to make sure that the parsing
of the initial part of the multipart request is only parsed once and initially
to distinguish between configuration and firmware uploads.
This removes the limitation that a file served from FLASH memory
needs to be smaller than the TCP buffer size. Now we serve up to
the TCP buffer size in the first go and then remember what parts
still need to be sent. As soon as the previous package has been
acked, the next chunk of data is copied from flash into the
TCP transmit buffer and gets sent. We take care only to send
the current TCP window size so no further fragmentation needs to
happen, thus optimizing transmission of the remainder.