default or selected kernelversion does not have config value CONFIG_DECNET_NF_GRABULATOR.
Result is shown for kernelversion 6.5.1

Routing message grabulator (for userland routing daemon)

modulename: dn_rtmsg.ko

configname: CONFIG_DECNET_NF_GRABULATOR

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>DECnet: Netfilter Configuration
└─>Routing message grabulator (for userland routing daemon)
In linux kernel since version 2.6.12  
Enable this module if you want to use the userland DECnet routing
daemon. You will also need to enable routing support for DECnet
unless you just want to monitor routing messages from other nodes.

source code: