Place MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH in alphabetical order
Place MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH in alphabetical order

The automatic merge of include/mbedtls/config.h had placed
MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH before
MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT.

NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls