control_endpoint does not correspond to documentation

[ilia1243]

Actual algorithm of Control plains resolution does not correspond to documentation.

See An example with mixed groups:

Actual result will be

Control plains:
   Internal: 192.168.0.2 (vrrp_ip[1])
   External: 10.101.0.1 (vrrp_ip[0])

Need to either fix algorithm or update documentation.