MINOR: peers: Add a warning about incompatible SSL config for the local peer

MINOR: peers: Add a warning about incompatible SSL config for the local peer

In peers section, it is possible to enable SSL for the local peer. In this
case, the bind line and the server line should both be configured. A
"default-server" directive may also be used to configure the SSL on the
server side. However there is no test to be sure the SSL is enabled on both
sides. It is an problem because the local resync performed during a reload
will be impossible and it is probably not the expected behavior.

So, it is now checked during the configuration validation. A warning message
is displayed if the SSL is not properly configured for the local peer.

This patch is related to issue #1799. It should probably be backported to 2.6.