Improve matching of empty message received

[BorisMorel]

Hi,

With PjSIP, empty messages received was not only "\r\n" (see below). So I change the strict matching by a regular.

Other question, why not response to this ?

Regards, Boris.

[jmillan]

This PR considers any message starting with CRLF a keep alive. The original implementation is intentional, considering CRLF a keep-alive beacon.

An option would we considering one or two CRLF as keep alive: /^(\r\n){1,2}$/

Being double CRLF defined here https://datatracker.ietf.org/doc/html/rfc5626#section-3.5.1

[UbiManu]

Hello When do you plan to implement this fix?

[jmillan]

Closed in favour of #791