Do not flood logs with modifications

Debugging logs have grown quite a bit for tell-based protocol
mostly due to us dumping modifications as part of the request
message. Log only the number of modification in the message,
which will make the logs quite a bit more readable.

Change-Id: I35961702b7bdd0e3f93cd03f05a0e443a14bf419
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>