Fix: Relayd and sessiond version check

Now only checks for the major version to be equal. After 2.1 stable
release, both components will adapt to the lowest minor version for the
same major version. For this, the session daemon now send it's version
values to the relayd so slight change in the protocol here.

For instance, a relayd 2.4 talking to a sessiond 2.8, the communication
and available feature will only be those of 2.4 version.

For a relayd let say 3.2 and a sessiond 2.2, the communication stops
right there since both major version differs.

Acked-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>