Better ebpf module errors

Report to the GUI and the logs, whether the modules have been found
or not, and if found, whether there have been any errors loading them.

Closes #868

daemon/core/ebpf.go

@@ -15,22 +15,29 @@ func LoadEbpfModule(module string) (m *elf.Module, err error) {
 		paths      = []string{
 			fmt.Sprint("/usr/local/lib", modulesDir),
 			fmt.Sprint("/usr/lib", modulesDir),
-			fmt.Sprint("/etc/opensnitchd"), // deprecated
+			fmt.Sprint("/etc/opensnitchd"), // Deprecated: will be removed in future versions.
 		}
 	)
-	modulesPath := ""
-	for _, p := range paths {
-		modulesPath = p
-		m = elf.NewModule(fmt.Sprint(modulesPath, "/", module))
+	modulePath := ""
+	moduleError := fmt.Errorf(`Module not found (%s) in any of the paths.
+You may need to install the corresponding package`, module)
 
-		if err = m.Load(nil); err == nil {
-			log.Info("[eBPF] module loaded: %s/%s", modulesPath, module)
+	for _, p := range paths {
+		modulePath = fmt.Sprint(p, "/", module)
+		log.Debug("[eBPF] trying to load %s", modulePath)
+		if !Exists(modulePath) {
+			continue
+		}
+		m = elf.NewModule(modulePath)
+
+		if m.Load(nil) == nil {
+			log.Info("[eBPF] module loaded: %s", modulePath)
 			return m, nil
 		}
-		log.Debug("ebpf module not found: %s, %s/%s", err, modulesPath, module)
-	}
-
-	return m, fmt.Errorf(`
+		moduleError = fmt.Errorf(`
 unable to load eBPF module (%s). Your kernel version (%s) might not be compatible.
 If this error persists, change process monitor method to 'proc'`, module, GetKernelVersion())
+	}
+
+	return m, moduleError
 }