LU-4423 lnet: Avoid forward declarations in nidstring.c

Backport of a patch from upstream  to remove some
forward declarations in nidstring.c. It appears
forward declarations are frowned on.

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Linux commit: fd17846d8d6acf991c660ed3498031c6451db61d

staging: lustre: libcfs/nidstrings: Avoid forward declarations

Avoid forward declarations by moving functions to a location
before they are referenced.

Signed-off-by: Sören Brinkmann <soeren.brinkmann@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: Ifeb5c6d61736b9d166966e76bb2a0224d77b602e
Reviewed-on: http://review.whamcloud.com/15084
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>