Do no test net_usleep in timing_selftest
Do no test net_usleep in timing_selftest

Timing belongs in libcrypto (due to havege depending on it)
while net.c was put in libtls (only test ssl servers use it)

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