modules/{http,watchdog}: fix stability problems

As first noted in commit d1a229ae, in some cases we do call chains that are not supported for JIT in LuaJIT.

I'm not 100% sure all of these are needed to comply, but the functions here are really small and probably not to be that heavily used, so I don't think it will be costly to interpret them (and avoiding crashes is more important).

In my tests this fixed occasional crashes when using http://*/trace/*

modules/http/http_trace.lua

@@ -23,6 +23,7 @@ local function serve_trace(h, _)
 	-- Create logging handler callback
 	local buffer = {}
 	local buffer_log_cb = ffi.cast('trace_log_f', function (_, msg)
+		jit.off(true, true) -- JIT for (C -> lua)^2 nesting isn't allowed
 		table.insert(buffer, ffi.string(msg))
 	end)
 
@@ -32,6 +33,7 @@ local function serve_trace(h, _)
 	local cond = condition.new()
 	local waiting, done = false, false
 	local finish_cb = ffi.cast('trace_callback_f', function (req)
+		jit.off(true, true) -- JIT for (C -> lua)^2 nesting isn't allowed
 		table.insert(buffer, req:selected_tostring())
 		if waiting then
 			cond:signal()