default or selected kernelversion does not have config value CONFIG_ISDN_CAPI_CAPIDRV_VERBOSE.
Result is shown for kernelversion 6.9.9

Verbose reason code reporting

configname: CONFIG_ISDN_CAPI_CAPIDRV_VERBOSE

Linux Kernel Configuration
└─>Device Drivers
└─>ISDN support
└─>CAPI 2.0 subsystem
└─>Verbose reason code reporting
In linux kernel since version 3.16 (release Date: 2014-08-03)  
If you say Y here, the capidrv interface will give verbose reasons
for disconnecting. This will increase the size of the kernel by 7 KB.
If unsure, say N.