datatype: use DTYPE_F_PREFIX only for IP address datatype

datatype: use DTYPE_F_PREFIX only for IP address datatype

DTYPE_F_PREFIX flag provides a hint to the netlink delinearize path to
use prefix notation.

It seems use of prefix notation in meta mark causes confusion, users
expect to see prefix in the listing only in IP address datatypes.

Untoggle this flag so (more lengthy) binop output such as:

  meta mark & 0xffffff00 == 0xffffff00

is used instead.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1739
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>