nfs plugin: Remove duplicated code.

nfs plugin: Remove duplicated code.

Changes include:

* Calculate nfs[234]_procedures_names_num at compile time.
* Made nfs_procedures_submit() more versatile, so it can be used from the Linux
  and the Solaris code.
* Switched to plugin_dispatch_values_secure(), since the code is using the same
  value_list_t for multiple values.
* Broke out nfs_submit_fields() from the Linux code. This removed quite a bit
  of code duplication between the v2/v3 code.
* Broke out nfs_read_kstat() which does the get_kstat_value() call in a loop
  rather than duplicating all the NFS procedure names.