Added DISABLE_DYNAMIC_RATE_LIMITING compilation toggle

[AM-Shafin]

Added DISABLE_DYNAMIC_RATE_LIMITING which should make the library use less CPU, costing only a tiny bit slow sending speed as described.

[Morcules]

Thank you for the contribution, I really appreciate the help

There’s just a few things missing:

• In process_packets, there’s a packet type that handles the delay signals .
• In send_packets there’s a usleep function handling rate limiting.
• Please remove last_index_checked and last_chunks_received_number from SwiftNetPendingMessage.

Again, thank you for your help. If you have any questions don't mind asking me. I will try to merge it ASAP.

[AM-Shafin]

Hello, thank you very much for making a detailed comment on the parts I've overlooked. It was really helpful since I'm very new to "contribution" and network related projects.

Right now I'm trying to work on the last point, about removing the 2 variables called last_index_checked and last_chunks_received_number from the struct SwiftNetPendingMessage{} , but if I search the project for their use, it seems these variables are being used quite a few times in process_packets.c file.

Apologies if asking the obvious: should I wrap the 2 stated variables in #ifndef DISABLE_DYNAMIC_RATE_LIMITING like I did for other parts? If so my code is ready to push online.

Thank you in advance for your patience!