Revert "generic: batman-adv: disable multicast optimizations for now"

This reverts commit 819758f4250af8820851945ba1a6c17748b0ab4b.

A proper fix is now available, therefore reverting this workaround.

targets/generic

@@ -5,8 +5,6 @@ config 'CONFIG_ALL_NONSHARED=y'
 config 'CONFIG_BUSYBOX_CUSTOM=y'
 config '# CONFIG_BUSYBOX_CONFIG_FEATURE_PREFER_IPV4_ADDRESS is not set'
 
-config '# CONFIG_KMOD_BATMAN_ADV_MCAST is not set'
-
 config 'CONFIG_PACKAGE_ATH_DEBUG=y'
 
 config 'CONFIG_TARGET_MULTI_PROFILE=y'