fix: workaround the ethernet_init warnings

Author: alisitsyn

tools/ignore_build_warnings.txt

@@ -4,6 +4,7 @@ Warning: Deprecated: Option '--flash_freq' is deprecated. Use '--flash-freq' ins
 Warning: Deprecated: Command 'sign_data' is deprecated. Use 'sign-data' instead.
 Warning: Deprecated: Command 'extract_public_key' is deprecated. Use 'extract-public-key' instead.
 warning: unknown kconfig symbol 'EXAMPLE_ETH_PHY_IP101' assigned to 'y' in .*
+WARNING: The following Kconfig variables were used in "if" clauses, but not.*
 library/error\.o
 /.*error\S*\.o
 .*error.*\.c\.obj