json: export non-static functions

Two non-static functions in virjson.c were missing their export info in
libvirt_private.syms, so they couldn't be used anywhere it the code (and
that's about to get changed).
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/libvirt_private.syms

@@ -1570,6 +1570,7 @@ virISCSIScanTargets;
 virJSONValueArrayAppend;
 virJSONValueArrayGet;
 virJSONValueArraySize;
+virJSONValueArraySteal;
 virJSONValueFree;
 virJSONValueFromString;
 virJSONValueGetArrayAsBitmap;
@@ -1580,6 +1581,7 @@ virJSONValueGetNumberLong;
 virJSONValueGetNumberUint;
 virJSONValueGetNumberUlong;
 virJSONValueGetString;
+virJSONValueIsArray;
 virJSONValueIsNull;
 virJSONValueNewArray;
 virJSONValueNewArrayFromBitmap;