BUG/MEDIUM: connection: sanitize PPv2 header length before parsing address information

Previously, if hdr_v2->len was less than the length of the protocol
specific address information we could have read after the end of the
buffer and initialize the sockaddr structure with junk.

Signed-off-by: KOVACS Krisztian <hidden@balabit.com>

[WT: this is only tagged medium since proxy protocol is only used from
 trusted sources]

This must be backported to 1.5.
(cherry picked from commit efd3aa93412648cf923bf3d2e171c0b84e9d7a69)
BUG/MINOR: stats: correctly set the request/response analysers

When enabling stats, response analysers were set on the request
analyser list, which 1) has no effect, and 2) means we don't have
the response analysers properly set.

In practice these response analysers are set when the connection
to the server or applet is established so we don't need/must not
set them here.

Fortunately this bug had no impact since the flags are distinct,
but it definitely is confusing.

It should be backported to 1.5.
(cherry picked from commit 5506e3f8b69927c1a381a268d5b0ca9907b363f5)