examples/network/sta2eth: Add comment explaining MIN_DHCP_PACKET_SIZE (IDFGH-12443)

[owenthewizard]

Is your feature request related to a problem?

I'm not sure how the value if MIN_DHCP_PACKET_SIZE was decided. In addition, it seems to be used when dealing with the size of an Ethernet frame, not a DHCP/UDP/IP packet.
AFAIK the minimum DHCP packet size is 236 bytes. I assume that the 285 bytes figure is adding the UDP/IP packet and Ethernet frame overhead. However, it would be nice to have a comment confirming this.

Describe the solution you'd like.

Add a comment, for example:

/**                                                                             
 * The minimum size of a DHCP packet is 236 bytes.                
 * This includes the DHCP header and the minimum-sized DHCP message, which is a DHCPDISCOVER or
 * DHCPREQUEST message with no options.
 */                                                                             
#define MIN_DHCP_PACKET_SIZE (236)

Describe alternatives you've considered.

No response

Additional context.

No response

[david-cermak]

Thank you for bringing this up! That's correct, the minimum DHCP packet size is 236 bytes, and the MIN_DHCP_PACKET_SIZE value indeed accounts for the additional overhead from the UDP, IP, and Ethernet headers.
Adding a comment as you suggested would certainly clarify things.

I'll make the necessary changes soon. At the moment, I'm also working on extending this example to support an additional (so-called) "wired" interface (besides Ethernet and USB) and to introduce support for WiFi softAP. Alongside this, I'll be renaming "wired" to something else, so that "sta2ap" option fits into the picture.