Update send_ttl mainly for server models. When a server model
receives a message, and the status is required to be replied
by the application, we need to set send_ttl to the msg context.
If send_ttl is not updated in btc, and the applcation does not
set the TTL either, then the status will be replied with TTL=0,
which may cause the client side (e.g. the phone App) failed to
receive the status.
Closes https://github.com/espressif/esp-idf/issues/5300
9eb66d49e4