BUG/MINOR: mux-h1: Fix the parsing of trailers

Unlike other H1 parsing functions, the 3rd parameter of the function
h1_measure_trailers() is the maximum number of bytes to read. For others
functions, it is the relative offset where to stop the parsing.

This patch must be backported to 1.9.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index 69a6e25..6c85c11 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -1219,7 +1219,7 @@
 				if (h1s->flags & H1S_F_HAVE_I_TLR)
 					goto skip_tlr_parsing;
 
-				ret = h1_measure_trailers(buf, *ofs, *ofs + max);
+				ret = h1_measure_trailers(buf, *ofs, max);
 				if (ret > data_space)
 					ret = (htx_is_empty(htx) ? -1 : 0);
 				if (ret <= 0)