kni: fix build with gcc 7.1

kni: fix build with gcc 7.1

build error:
.../dpdk/build/build/lib/librte_eal/linuxapp/kni/igb_main.c:
  In function ‘igb_kni_probe’:
.../dpdk/build/build/lib/librte_eal/linuxapp/kni/igb_main.c:2483:30:
  error: ‘%d’ directive output may be truncated writing between 1 and 5
  bytes into a region of size between 0 and 11
  [-Werror=format-truncation=]
        "%d.%d, 0x%08x, %d.%d.%d",
                              ^~
.../dpdk/build/build/lib/librte_eal/linuxapp/kni/igb_main.c:2483:8:
  note: directive argument in the range [0, 65535]
        "%d.%d, 0x%08x, %d.%d.%d",
        ^~~~~~~~~~~~~~~~~~~~~~~~~
.../dpdk/build/build/lib/librte_eal/linuxapp/kni/igb_main.c:2481:4:
  note: ‘snprintf’ output between 23 and 43 bytes into a destination of
  size 32
    snprintf(adapter->fw_version,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        sizeof(adapter->fw_version),
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        "%d.%d, 0x%08x, %d.%d.%d",
        ~~~~~~~~~~~~~~~~~~~~~~~~~~
        fw.eep_major, fw.eep_minor, fw.etrack_id,
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        fw.or_major, fw.or_build, fw.or_patch);
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixed by increasing buffer size to 43 as suggested in compiler log.

Fixes: b9ee370557f1 ("kni: update kernel driver ethtool baseline")
Cc: stable@dpdk.org
Reported-by: Nirmoy Das <ndas@suse.de>
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Reviewed-by: Markos Chandras <mchandras@suse.de>