net: netconsole: do not pass userdata up to the tail

Do not pass userdata to send_msg_fragmented, since we can get it later.

This will be more useful in the next patch, where send_msg_fragmented()
will be split even more, and userdata is only necessary in the last
function.

Suggested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>