msg/async: Encode message once features are set

msg/async: Encode message once features are set

Modify send_message to check if features are set before trying to encode a
message.
If features are not set at this point, we will encode the message at a
later stage (in write_event) when the connection will be in ready state
which implies that the features will definitely be set.

Fixes: https://tracker.ceph.com/issues/52657
Signed-off-by: Aishwarya Mathuria <amathuri@redhat.com>