IED Server/Goose: Fix the 'Goose Ethernet Interface Id' allocation

Issue:
In the case of 'GooseInterfaceId' initialization for all GOOSE
publishers (API function: IedServer_setGooseInterfaceId()), only the pointer of
the character string is saved and used for the next operations.
If the corresponding memory is cleared or overwritten in the
application program, a segfault may occurred in libiec61850.

Proof:
In the 'server_example_goose.c' example, if we used a temporary
allocated memory to store the 'ethernetIfcId', the bug will occur:

        /* set GOOSE interface for all GOOSE publishers (GCBs) */
    +   unsigned int ethernet_interface_id_length = strnlen(ethernetIfcID, 32);
    +   char * tmp_ethernet_interface_id = calloc(sizeof(char), ethernet_interface_id_length + 1);
    +   memcpy(tmp_ethernet_interface_id, ethernetIfcID, ethernet_interface_id_length);
    +
        IedServer_setGooseInterfaceId(iedServer, tmp_ethernet_interface_id);
    +
    +   explicit_bzero(tmp_ethernet_interface_id, ethernet_interface_id_length);
    +   free(tmp_ethernet_interface_id);

(This issue was discovered during the rewriting of 'server_example_goose'
in Python, with the Swig wrapper: the allocated memory for
'ethernetIfcID' parameter in the Swig wrapper is automatically reused)

Fix:
The 'gooseInterfaceId' attribute of 'MmsMapping' in libiec61850 must be a new
allocated memory (with the use of 'StringUtils_copyString()') and deallocated
in the 'MmsMapping_destroy()' function.

src/iec61850/server/impl/ied_server.c

@@ -1692,6 +1692,6 @@ void
 IedServer_setGooseInterfaceId(IedServer self, const char* interfaceId)
 {
 #if (CONFIG_INCLUDE_GOOSE_SUPPORT == 1)
-    self->mmsMapping->gooseInterfaceId = interfaceId;
+    self->mmsMapping->gooseInterfaceId = StringUtils_copyString(interfaceId);
 #endif
 }

src/iec61850/server/mms_mapping/mms_mapping.c

@@ -2015,6 +2015,7 @@ MmsMapping_destroy(MmsMapping* self)
 
 #if (CONFIG_INCLUDE_GOOSE_SUPPORT == 1)
     LinkedList_destroyDeep(self->gseControls, (LinkedListValueDeleteFunction) MmsGooseControlBlock_destroy);
+    if (self->gooseInterfaceId) GLOBAL_FREEMEM(self->gooseInterfaceId);
 #endif
 
 #if (CONFIG_IEC61850_SAMPLED_VALUES_SUPPORT == 1)