zephyr: Switch to microkernel, required for network to work in background.

zephyr/Makefile.zephyr

@@ -14,10 +14,11 @@
 # limitations under the License.
 #
 
-KERNEL_TYPE = nano
+KERNEL_TYPE = micro
 # BOARD must be passed on command line from main Makefile
 #BOARD =
 CONF_FILE = prj.conf
+MDEF_FILE = prj.mdef
 
 #export SOURCE_DIR = $(ZEPHYR_BASE)/samples/static_lib/hello_world
 export LDFLAGS_zephyr += -L$(CURDIR)

zephyr/prj.mdef

+% Application       : MicroPython
+
+% TASK NAME  PRIO ENTRY STACK GROUPS
+% ==================================
+  TASK MAIN  7    main  4096 [EXE]