ssl: When no SNI is present, use the _server_ IP as 'servername'

Previously this used the client IP ... which is really annoying and
I don't see what use case this would fit.

Matching on the server IP is already possible using the v_target_ip
match module. However matching on the IP of servername allows better
control because it will be the IP only if the client doesn't do SNI
while v_target_ip will always match even if the client sent an explicit
name. So this way you can use IP matching only has a fallback for non-SNI.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>