zebra: Fix display of `show ip import-check A.B.C.D`

zebra: Fix display of `show ip import-check A.B.C.D`

The 'show ip import-check A.B.C.D` code was generating
a /32 prefix for comparison.  Except import-check was
being used by bgp to track networks.  So they could
have received a /24( or anything the `network A.B.C.D/M`
statement specifies ).

Consequently when we do a `show ip import-check A.B.C.D`
we would never find the network but a `show ip import-check |
grep A.B.C.D` would find it.

Fix the exact comparison to a match.

For the `show ip nht A.B.C.D` case we are comparing
a /32 to a /32 so prefix_match will work still.
While a `show ip import-check A.B.C.D` will now show
the expected behavior as well.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>