Set name for all the isc_mem context

The memory context for managers and dlz_dlopen_driver units had no name
and that was causing trouble with the statistics channel output.  Set
the name for the two memory context that were missing a proper name.

(cherry picked from commit 5d264b3329)

bin/named/dlz_dlopen_driver.c

@@ -223,6 +223,7 @@ dlopen_dlz_create(const char *dlzname, unsigned int argc, char *argv[],
 	}
 
 	isc_mem_create(&mctx);
+	isc_mem_setname(mctx, "named_dlz");
 	cd = isc_mem_get(mctx, sizeof(*cd));
 	*cd = (dlopen_data_t){
 		.mctx = mctx,

bin/named/main.c

@@ -641,6 +641,7 @@ printversion(bool verbose) {
 	printf("threads support is enabled\n");
 
 	isc_mem_create(&mctx);
+	isc_mem_setname(mctx, "main");
 	result = dst_lib_init(mctx, named_g_engine);
 	if (result == ISC_R_SUCCESS) {
 		isc_buffer_init(&b, buf, sizeof(buf));

lib/isc/managers.c

@@ -22,6 +22,7 @@ isc_managers_create(isc_mem_t **mctxp, uint32_t workers,
 	REQUIRE(mctxp != NULL && *mctxp == NULL);
 	isc_mem_create(mctxp);
 	INSIST(*mctxp != NULL);
+	isc_mem_setname(*mctxp, "managers");
 
 	REQUIRE(loopmgrp != NULL && *loopmgrp == NULL);
 	isc_loopmgr_create(*mctxp, workers, loopmgrp);