default or selected kernelversion does not have config value CONFIG_MPTCP_KUNIT_TESTS.
Result is shown for kernelversion 6.9.8

This builds the MPTCP KUnit tests

modulename: mptcp_crypto_test.ko

configname: CONFIG_MPTCP_KUNIT_TESTS

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>This builds the MPTCP KUnit tests
In linux kernel since version 5.1 (release Date: 2019-05-05)  
Currently covers the MPTCP crypto and token helpers.
Only useful for kernel devs running KUnit test harness and are not
for inclusion into a production build.

For more information on KUnit and unit tests in general please refer
to the KUnit documentation in Documentation/dev-tools/kunit/.

If unsure, say N.

source code: