set_elem: Fix printing of verdict map elements

set_elem: Fix printing of verdict map elements

Elements' data was printed as type DATA_VALUE no matter the actual type.
For verdicts, this meant no printing at all (because reg->len is either
zero or garbage).

To fix this, nftnl_set_elem_snprintf_default() needs type info held in
struct nftnl_set. Pass it via parameter to that function, make it
non-static and call it from nftnl_set_snprintf_default() instead of the
generic nftnl_set_elem_snprintf(). This way no changes have to be done
to exported functions, also the output type is already defined when
nftnl_set_snprintf_default() runs so checking type value again is
pointless.

Signed-off-by: Phil Sutter <phil@nwl.cc>