LU-4353 strncmp: Replace incorrect strncmp()s with strcmp()

LU-4353 strncmp: Replace incorrect strncmp()s with strcmp()

This patch fixes a few places where strncmp() is used but strcmp()
was meant. It also corrects calls to strncmp() in functions
mdd_declare_xattr_del() and mgs_setparam().

Change-Id: I6f0fa4230bca10e8e7b310783bb89628a6eb788f
Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Reviewed-on: http://review.whamcloud.com/8702
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>