zebra: "ip import-table" display is hosed

zebra: "ip import-table" display is hosed

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
Reviewed-by:   Don Slice <dslice@cumulusnetworks.com>
Ticket: CM-13020

Now that we have evpn we have the following AFIs

 /* Address family numbers from RFC1700. */
 typedef enum {
   AFI_IP  = 1,
   AFI_IP6 = 2,
   AFI_ETHER = 3,                /* RFC 1700 has "6" for 802.* */
   AFI_MAX = 4
 } afi_t;

The import-table code was treating the afi as a flag which was fine
before when the only choices were 1 and 2 but now that we have #3 that
doesn't work. The fix is to change zebra_import_table_used to a
[AFI_MAX][ZEBRA_KERNEL_TABLE_MAX] array to track if import-table is
enabled.