LU-6245 libcfs: move struct netstrfns to nidstr.h

LU-6245 libcfs: move struct netstrfns to nidstr.h

The reason struct netstrfns exist in nidstrings.c
was to avoid forward decleration errors. The best
way to handle this instead is to move this structure
to a header file. Since this structure is used in
the userland utilities as well so we place it in
nidstr.h which is exposed to userland.

Change-Id: I02610e90a8d252defc9e8778f9f86be5ab2de9fe
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: http://review.whamcloud.com/15083
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>