When the user enters each "peer" node, the related object is created if
not yet existing, and its updated config is applied (connect()) upon
exiting the node (cbc_peer_apply_cfg_chg()). When connect happens, it
needs to obtain the local IP address from the main protocol node
(cbsp|sbcap)", which means it must be configured beforehand, otherwise
the peers connect using the default values.
Hence, it makes no sense to configure peers if the main protocol
information has not yet been configured. The usual example configs as
well as the write-config VTY commands provide correct order of things.
Catch and forbid the user providing a config file where the peers are
configured before the main protocol nodes.
Related: OS#6154
Change-Id: I678f9e6715c85b1eb9116cc892f1a8299577c0c2