[mbedtls] update mbedtls-config.h to fix build (#3338)
[mbedtls] update mbedtls-config.h to fix build (#3338)

- Add stdio.h for snprintf.

- When `MBEDTLS_ECP_ALT` is defined, need to define mbedtls_ecp_restart_ctx
for build to succeed.

abtink/openthread,srickardti/openthread,erja-gp/openthread,openthread/openthread,jwhui/openthread,lanyuwen/openthread,erja-gp/openthread,openthread/openthread,lanyuwen/openthread,jwhui/openthread,chshu/openthread,turon/openthread,lanyuwen/openthread,chshu/openthread,erja-gp/openthread,chshu/openthread,chshu/openthread,lanyuwen/openthread,abtink/openthread,srickardti/openthread,lanyuwen/openthread,turon/openthread,bukepo/openthread,librasungirl/openthread,turon/openthread,openthread/openthread,bukepo/openthread,erja-gp/openthread,jwhui/openthread,librasungirl/openthread,erja-gp/openthread,srickardti/openthread,bukepo/openthread,bukepo/openthread,chshu/openthread,erja-gp/openthread,srickardti/openthread,librasungirl/openthread,openthread/openthread,abtink/openthread,turon/openthread,chshu/openthread,librasungirl/openthread,jwhui/openthread,abtink/openthread,lanyuwen/openthread