devlink: add devlink_fmsg_dump_skb() function

Add devlink_fmsg_dump_skb() function that adds some diagnostic
information about skb (like length, pkt type, MAC, etc) to devlink
fmsg mechanism using bunch of devlink_fmsg_put() function calls.

Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>