MINOR: h1: Add the flag H1_MF_NO_PHDR to not add pseudo-headers during parsing

Some pseudo-headers are added during the headers parsing, mainly for the mux
H2. With this flag, it is possible to not add them. This avoid some boring
filtering in the mux H1.
diff --git a/include/types/h1.h b/include/types/h1.h
index af5c896..d3e4426 100644
--- a/include/types/h1.h
+++ b/include/types/h1.h
@@ -147,6 +147,7 @@
 #define H1_MF_CONN_UPG          0x00000080 // message contains "connection: upgrade"
 #define H1_MF_XFER_LEN          0x00000100 // message xfer size can be determined
 #define H1_MF_XFER_ENC          0x00000200 // transfer-encoding is present
+#define H1_MF_NO_PHDR           0x00000400 // don't add pseudo-headers in the header list
 
 /* Note: for a connection to be persistent, we need this for the request :
  *   - one of CLEN or CHNK