Default configure with nss instead of cryptopp

The -n option for nss has been changed to -c to give the
chance to pass cryptopp flag to configure

Signed-off-by: Federico Gimenez <fgimenez@coit.es>
Merge pull request #2761 from fgimenez/do-autogen-defaults-to-nss

do_autogen.sh: default configure with nss instead of cryptopp

Reviewed-by: Sage Weil <sage@redhat.com>