[bsc/idu]: keep netfilter/ipsec as modules

It seems like the kernel/package/upgrade/... proceess doesn't deal well
with the fact that some options used to be modules, which are now
built-in.  Let's keep it as modules for the time being.

recipes-bsp/linux/files/sysmocom-bsc/defconfig

@@ -560,13 +560,13 @@ CONFIG_PACKET_DIAG=m
 CONFIG_UNIX=y
 CONFIG_UNIX_DIAG=m
 CONFIG_XFRM=y
-CONFIG_XFRM_ALGO=y
-CONFIG_XFRM_USER=y
+CONFIG_XFRM_ALGO=m
+CONFIG_XFRM_USER=m
 CONFIG_XFRM_SUB_POLICY=y
 CONFIG_XFRM_MIGRATE=y
 CONFIG_XFRM_STATISTICS=y
-CONFIG_XFRM_IPCOMP=y
-CONFIG_NET_KEY=y
+CONFIG_XFRM_IPCOMP=m
+CONFIG_NET_KEY=m
 CONFIG_NET_KEY_MIGRATE=y
 CONFIG_INET=y
 CONFIG_IP_MULTICAST=y
@@ -592,11 +592,11 @@ CONFIG_IP_PIMSM_V2=y
 # CONFIG_ARPD is not set
 CONFIG_SYN_COOKIES=y
 CONFIG_NET_IPVTI=m
-CONFIG_INET_AH=y
-CONFIG_INET_ESP=y
-CONFIG_INET_IPCOMP=y
-CONFIG_INET_XFRM_TUNNEL=y
-CONFIG_INET_TUNNEL=y
+CONFIG_INET_AH=m
+CONFIG_INET_ESP=m
+CONFIG_INET_IPCOMP=m
+CONFIG_INET_XFRM_TUNNEL=m
+CONFIG_INET_TUNNEL=m
 CONFIG_INET_XFRM_MODE_TRANSPORT=y
 CONFIG_INET_XFRM_MODE_TUNNEL=y
 CONFIG_INET_XFRM_MODE_BEET=y
@@ -658,8 +658,8 @@ CONFIG_BRIDGE_NETFILTER=y
 #
 # Core Netfilter Configuration
 #
-CONFIG_NETFILTER_NETLINK=y
-CONFIG_NETFILTER_NETLINK_ACCT=y
+CONFIG_NETFILTER_NETLINK=m
+CONFIG_NETFILTER_NETLINK_ACCT=m
 CONFIG_NETFILTER_NETLINK_QUEUE=m
 CONFIG_NETFILTER_NETLINK_LOG=m
 CONFIG_NF_CONNTRACK=m