DOC: config: 'http-send-name-header' option may be used in default section

Both doc and code agree on the fact that 'http-send-name-header' option
could be used in default section, but the keyword compatibility matrix
in configuration.txt reported the opposite.

This could be backported to all stable versions.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index ca1aa44..220483a 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -4177,7 +4177,7 @@
 http-request                              X (!)      X         X         X
 http-response                             X (!)      X         X         X
 http-reuse                                X          -         X         X
-http-send-name-header                     -          -         X         X
+http-send-name-header                     X          -         X         X
 id                                        -          X         X         X
 ignore-persist                            -          -         X         X
 load-server-state-from-file               X          -         X         X