REORG: include: split common/http-hdr.h into haproxy/http-hdr{,-t}.h

There's only one struct and 2 inline functions. It could have been
merged into http.h but that would have added a massive dependency on
the hpack parts for nothing, so better keep it this way since hpack
is already freestanding and portable.
diff --git a/src/h1.c b/src/h1.c
index f30e489..f143db9 100644
--- a/src/h1.c
+++ b/src/h1.c
@@ -13,7 +13,7 @@
 #include <ctype.h>
 #include <haproxy/api.h>
 #include <common/h1.h>
-#include <common/http-hdr.h>
+#include <haproxy/http-hdr.h>
 
 #include <proto/channel.h>
 
diff --git a/src/h2.c b/src/h2.c
index fa72e1c..c59c3f2 100644
--- a/src/h2.c
+++ b/src/h2.c
@@ -29,7 +29,7 @@
 #include <haproxy/api.h>
 #include <haproxy/http.h>
 #include <common/h2.h>
-#include <common/http-hdr.h>
+#include <haproxy/http-hdr-t.h>
 #include <import/ist.h>
 #include <types/global.h>
 
diff --git a/src/hpack-enc.c b/src/hpack-enc.c
index bf7336b..21e28f6 100644
--- a/src/hpack-enc.c
+++ b/src/hpack-enc.c
@@ -31,7 +31,7 @@
 #include <string.h>
 
 #include <common/hpack-enc.h>
-#include <common/http-hdr.h>
+#include <haproxy/http-hdr-t.h>
 #include <import/ist.h>
 
 #include <types/global.h>