LU-3474 mdt: mdt_links_read() to return linkea_init() errors

Handle linkea_init() errors.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I2095084d6fb1ba71d15c0b63c183a642ebcf4200
Reviewed-on: http://review.whamcloud.com/6772
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>