DOC: clarify some points around http-send-name-header's behavior

The directive causes existing an header to be removed, which is not
explicitly mentioned though already being relied on, and also mention
the fast that it should not be used to modify transport level headers
and that doing it on Host is more than border-line and definitely not
a supported long-term option eventhough it currently works.

(cherry picked from commit 81bef7e89993c963d934eab21cca744cb6a6cb03)
Signed-off-by: Willy Tarreau <w@1wt.eu>
1 file changed