iprule: refactor print_rule() to use leading space before printing attribute

iprule: refactor print_rule() to use leading space before printing attribute

When printing the actions, we avoid adding the trailing space after the
attribute. Possibly because we expect the action to be the last output
on the line and not end with a space.

But for FR_ACT_TO_TBL nothing is printed. That means, we add double
spaces if a protocol is printed as well:

    # ip rule add priority 10 protocol 10 type 1

will be printed as

    10:     from all lookup 1  proto mrt

The only visible effect of the patch is to avoid the double-space and
avoid a trailing space if the action is FR_ACT_TO_TBL.

Signed-off-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>