MINOR: trace: make trace sources read_mostly

The trace sources are checked at plenty of places in the code and their
contents only change when trace status changes, let's mark them read_mostly.

src/mux_fcgi.c

@@ -335,7 +335,7 @@ static const struct name_desc fcgi_trace_decoding[] = {
 	{ /* end */ }
 };
 
-static struct trace_source trace_fcgi = {
+static struct trace_source trace_fcgi __read_mostly = {
 	.name = IST("fcgi"),
 	.desc = "FastCGI multiplexer",
 	.arg_def = TRC_ARG1_CONN,  // TRACE()'s first argument is always a connection

src/mux_h1.c

@@ -244,7 +244,7 @@ static const struct name_desc h1_trace_decoding[] = {
 	{ /* end */ }
 };
 
-static struct trace_source trace_h1 = {
+static struct trace_source trace_h1 __read_mostly = {
 	.name = IST("h1"),
 	.desc = "HTTP/1 multiplexer",
 	.arg_def = TRC_ARG1_CONN,  // TRACE()'s first argument is always a connection

src/mux_h2.c

@@ -372,7 +372,7 @@ static const struct name_desc h2_trace_decoding[] = {
 	{ /* end */ }
 };
 
-static struct trace_source trace_h2 = {
+static struct trace_source trace_h2 __read_mostly = {
 	.name = IST("h2"),
 	.desc = "HTTP/2 multiplexer",
 	.arg_def = TRC_ARG1_CONN,  // TRACE()'s first argument is always a connection

src/mux_pt.c

@@ -76,7 +76,7 @@ static const struct name_desc pt_trace_decoding[] = {
 	{ /* end */ }
 };
 
-static struct trace_source trace_pt = {
+static struct trace_source trace_pt __read_mostly = {
 	.name = IST("pt"),
 	.desc = "Passthrough multiplexer",
 	.arg_def = TRC_ARG1_CONN,  // TRACE()'s first argument is always a connection