ksmbd: select ASN1 explicitly to reduce dependencies

ksmbd: select ASN1 explicitly to reduce dependencies

ksmbd requires ASN.1 grammar compiler so it depends on CONFIG_ASN1. It
should select kmod-asn1-decoder for above reason.

Due to some problems with kmod-asn1-decoder in the past ksmbd was
selecting kmod-nf-nathelper-extra instead. That was affecting network
performance in kernel as each loaded conntrack module adds some overhead
to packets processing.

Fix this unwanted side effect by depending on kmod-asn1-decoder
directly.

Link: http://lists.openwrt.org/pipermail/openwrt-devel/2023-January/040298.html
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>