Increase UDP record packing time in ssl-opt.sh
Increase UDP record packing time in ssl-opt.sh

The UDP tests involving the merging of multiple records into single
datagrams accumulate records for 10ms, which can be less than the
total flight preparation time if e.g. the tests are being run with
valgrind.

This commit increases the packing time for the relevant tests
from 10ms to 50ms.

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