multithreading support in librelp (or rsyslog relp input)

[jay7x]

RELP input was eating 100% of single CPU core under my load (about 100k msg/s). It was unable to process message queue. So I switched to imptcp which able to run on multiple CPU cores. It'd be great if librelp (or imrelp) were able to run on multiple CPU cores.

If multithreading implementation is problematic it may be good enough to isolate at least every RELP input. Then it will be possible to start multiple inputs and spread load over them (using message sharding e.g.).