Update android build after bindings rewrite

The sigrok bindings depend on libffi.so, which is an unversioned shared
object, so add it to the whitelist of libraries to install into the APK.

android/custom_rules.xml

@@ -38,6 +38,7 @@
 		<copylibs todir="${native.libs.absolute.dir}" property="bundled_libs">
 			<fileset dir="${pulseview-build-path}/libs"/>
 			<include name="libgnustl_shared.so"/>
+			<include name="libffi.so"/>
 			<exclude name="lib*.so"/>
 		</copylibs>
 		<copy todir="${native.libs.absolute.dir}">