add a --single-public-ip argument to ctdbd to specify the ip address

add a --single-public-ip argument to ctdbd to specify the ip address
used in single public ip address mode.
when using this argument, --public-interface must also be used.

add a vnn structure to the ctdb context to describe the single public ip
address

update the killtcp control in the daemon that if a socketpair that is to
be killed does not match a normal public address it checks if the
destination address maches the single public ip address and if so uses
that vnn structure from the ctdb context

this allows killtcp to kill also connections to the single public ip
instead of only normal public addresses