Fixed BZ920444 by using macros to handle nfs parameter changes.

Fixed BZ920444 by using macros to handle nfs parameter changes.

* tapset/linux/nfs_proc.stpm: New file.
* tapset/linux/nfs_proc.stp: Remove __i2n_ip_proto(),
  __nfs_read_data_info(), and __nfs_write_data_info() functions. Callers
  of those functions now use new macros in nfs_proc.stpm. The advantage
  the macros have, besides clarity, is that they preserve type
  information. Kernel commit 0b7c01533aa9f4a228d07d2768d084acb3a387bc
  changed the commit functions to take a nfs_commit_data structure instead
  of a nfs_write_data_structure. Because functions lose type information,
  systemtap didn't notice this change.