return error code from wolfSSL_RefWithMutexUnlock() to expose result to caller;
fix endianness bug in src/x509.c:wolfSSL_X509_add_ext() (fixes failing test_wolfSSL_X509_add_ext on BE targets);
fix possible file handle leak in tests/api.c:test_wolfSSL_d2i_X509_REQ() (reported by clang-tidy);
in wolfssl/ssl.h, define CONST_NUM_ERR_WOLFSSL_SUCCESS, so that WOLFSSL_SUCCESS can be benignly miswrapped in WC_NO_ERR_TRACE().
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