distro_bootcmd: set devtype for dhcp boot

Set $devtype for DHCP boot, which can be handy for the boot.scr
for detection of devtype used (for example, when the same boot.scr is
used for both mmc/dhcp boot):

if test ${devtype} = "dhcp"; then
	...
fi

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>

include/config_distro_bootcmd.h

@@ -369,6 +369,7 @@
 #endif
 #define BOOTENV_DEV_DHCP(devtypeu, devtypel, instance) \
 	"bootcmd_dhcp=" \
+		"setenv devtype " #devtypel "; " \
 		BOOTENV_RUN_NET_USB_START \
 		BOOTENV_RUN_PCI_ENUM \
 		"if dhcp ${scriptaddr} ${boot_script_dhcp}; then " \