default or selected kernelversion does not have config value CONFIG_NET_DSA_MV88E6123.
Result is shown for kernelversion 5.4.229

Marvell 88E6123/6161/6165 ethernet switch chip support

configname: CONFIG_NET_DSA_MV88E6123

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Distributed Switch Architecture drivers
└─>Marvell 88E6123/6161/6165 ethernet switch chip support
In linux kernel since version 4.6 (release Date: 2016-05-15)  
This enables support for the Marvell 88E6123/6161/6165
ethernet switch chips.