BUG/MEDIUM: server: properly initialize PROXY v2 TLVs

BUG/MEDIUM: server: properly initialize PROXY v2 TLVs

The PROXY v2 TLVs were not properly initialized when defined with
"set-proxy-v2-tlv-fmt" keyword, which could have caused a crash when
validating the configuration or malfunction (e.g. when used in
combination with "server-template" and/or "default-server").

The issue was introduced with commit 6f4bfed3a ("MINOR: server: Add
parser support for set-proxy-v2-tlv-fmt").

This should be backported up to 2.9.

(cherry picked from commit 6838fe43a320cf090892451ee907967666b626e5)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 77b48b2ae0dba907115c304ea78187a0f77e60c0)
Signed-off-by: Willy Tarreau <w@1wt.eu>