BUG/MINOR: connection: always send address-less LOCAL PROXY connections

BUG/MINOR: connection: always send address-less LOCAL PROXY connections

Commit 7f26391bc5 ("BUG/MINOR: connection: make sure to correctly tag
local PROXY connections") revealed that some implementations do not
properly ignore addresses in LOCAL connections (at least Dovecot was
spotted). More context information in the thread below:

   https://www.mail-archive.com/haproxy@formilux.org/msg36890.html

The patch above was using LOCAL on top of local addresses in order to
minimize the risk of breakage but revealed worse than a clean fix. So
let's partially revert it and send pure LOCAL connections instead now.

After a bit of observation, this patch should be progressively backported
to stable branches. However if it reveals new breakage, the backport of
the patch above will have to be reverted from stable branches while other
products work on fixing their code based on the master branch.

(cherry picked from commit 02c88036a61e09d0676a2b6b4086af677b023b94)
Signed-off-by: Willy Tarreau <w@1wt.eu>