[NFSD] uninline nfsd4_op_name()

There doesn't seem to be a compelling reason why nfsd4_op_name() is
marked as "inline":

It's only used in a dprintk(), and as long as it has only one caller
non-ancient gcc versions anyway inline it automatically.

This patch fixes the following compile error with gcc 3.4:

  ...
    CC      fs/nfsd/nfs4proc.o
  nfs4proc.c: In function `nfsd4_proc_compound':
  nfs4proc.c:854: sorry, unimplemented: inlining failed in call to
  nfs4proc.c:897: sorry, unimplemented: called from here
  make[3]: *** [fs/nfsd/nfs4proc.o] Error 1

Reported-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
[ Also made it "const char *"  - Linus]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>