package/gensio: add avahi optional dependency

avahi-client is an optional dependency which is enabled by default since
version 2.2.0 and
https://github.com/cminyard/gensio/commit/5ab117c9743fd4719f610cf9f1ba45023cc25d7c

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit f0a1d47f6fe6bda3b18b3fcfca37757b37695dbb)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gensio/gensio.mk

@@ -9,6 +9,7 @@ GENSIO_SITE = http://downloads.sourceforge.net/project/ser2net/ser2net
 GENSIO_LICENSE = LGPL-2.1+ (library), GPL-2.0+ (tools)
 GENSIO_LICENSE_FILES = COPYING.LIB COPYING
 GENSIO_INSTALL_STAGING = YES
+GENSIO_DEPENDENCIES = $(if $(BR2_PACKAGE_AVAHI_LIBAVAHI_CLIENT),avahi)
 GENSIO_CONF_OPTS = \
 	--without-openipmi \
 	--without-swig \