ffmpeg: enable gnutls support in libffmpeg-full

Provides access to services requiring a secure connection.

Chosen over openssl for license reason (can't redistribute). To my
knowledge, libressl will have the same issue.

mbed-tls is the only other ssl/tls provider, and this package is
complicated enough.

Signed-off-by: Ian Leonard <antonlacon@gmail.com>

multimedia/ffmpeg/Makefile

@@ -345,7 +345,7 @@ endef
 define Package/libffmpeg-full
 $(call Package/libffmpeg/Default)
  TITLE+= (full)
- DEPENDS+= +alsa-lib +PACKAGE_libopus:libopus \
+ DEPENDS+= +alsa-lib +libgnutls +PACKAGE_libopus:libopus \
     +SOFT_FLOAT:shine \
     +!SOFT_FLOAT:lame-lib \
     +PACKAGE_libx264:libx264 \
@@ -471,6 +471,7 @@ ifeq ($(BUILD_VARIANT),full)
 	)
 
 	FFMPEG_CONFIGURE+= \
+		--enable-gnutls \
 		--enable-avresample \
 		$(if $(CONFIG_BUILD_PATENTED),, \
 			$(call FFMPEG_DISABLE,decoder,$(FFMPEG_PATENTED_DECODERS)) \