tests: logging: log_links: Set CONFIG_LOG_DOMAIN_NAME in the test

Test was assuming that domain name is empty but on some
SoC CONFIG_LOG_DOMAIN_NAME is set by default and test
was failing. Add setting of domain name to test
configuration to ensure that same name is used for all
platforms.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>