utils: wrap libyang utils in velia::utils

The functions in utils/libyang.cpp were not inside velia::utils
namespace. This was bothering me for some time but I was too lazy.
Now I am going to perform a little refactor to those two functions
so perhaps the time is now.

Change-Id: I077c06b700d0529515595a7b85a87550796d8b54
diff --git a/src/utils/libyang.cpp b/src/utils/libyang.cpp
index 3f32575..d018a09 100644
--- a/src/utils/libyang.cpp
+++ b/src/utils/libyang.cpp
@@ -2,6 +2,8 @@
 #include <libyang/Tree_Data.hpp>
 #include "utils/libyang.h"
 
+namespace velia::utils {
+
 const char* getValueAsString(const libyang::S_Data_Node& node)
 {
     if (!node || node->schema()->nodetype() != LYS_LEAF) {
@@ -20,3 +22,4 @@
 
     return set->data().front();
 }
+}