package/mosquitto: libwebsockets support needs external loop support

When libwebsockets is enabled, mosquitto broker is built with websocket
support, but its code requires libwebsockets being built with external
loop option - otherwise, mosquitto gives a compile-time warning hinting
to unusable websocket support:

https://github.com/eclipse/mosquitto/commit/1b24f625ea4ee77f3c4796ec2233d059f8c7977e

To fix this, select the BR2_PACKAGE_LIBWEBSOCKETS_EXT_POLL option.

Signed-off-by: Luca Pesce <luca.pesce@vimar.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/mosquitto/Config.in

@@ -25,6 +25,7 @@ config BR2_PACKAGE_MOSQUITTO_BROKER
 	depends on BR2_USE_MMU # fork()
 	depends on !BR2_STATIC_LIBS # include <dlfcn.h>
 	depends on BR2_PACKAGE_MOSQUITTO
+	select BR2_PACKAGE_LIBWEBSOCKETS_EXT_POLL if BR2_PACKAGE_LIBWEBSOCKETS
 	help
 	  Build and install the mosquitto broker onto target.