pkg/wakaama: Move client mode flag to package

As the only implementation available in RIOT of LwM2M is the client, it
makes no sense to set this flag in every application.

examples/wakaama/Makefile

@@ -39,9 +39,6 @@ USEPKG += wakaama
 # Uncomment to indicate that the server is a LwM2M bootstrap server
 # CFLAGS += -DCONFIG_LWM2M_BOOTSTRAP=1
 
-# NOTE: Use wakaama in client mode
-CFLAGS += -DLWM2M_CLIENT_MODE
-
 include $(RIOTBASE)/Makefile.include
 
 # Configure server via CFLAGS only is not done via Kconfig

pkg/wakaama/Makefile.include

@@ -3,6 +3,9 @@ DIRS += $(RIOTBASE)/pkg/wakaama/contrib
 INCLUDES += -I$(RIOTBASE)/pkg/wakaama/include
 INCLUDES += -I$(PKGDIRBASE)/wakaama
 
+# NOTE: Use wakaama in client mode
+CFLAGS += -DLWM2M_CLIENT_MODE
+
 # Translate 'CONFIG_' options to package specific flags. This checks if the
 # option is being set via Kconfig or CFLAGS
 ifneq (,$(or $(CONFIG_LWM2M_BOOTSTRAP),$(filter -DCONFIG_LWM2M_BOOTSTRAP=1,$(CFLAGS))))