nfsd: add a nfserrno mapping for -E2BIG to nfserr_fbig

I saw this pop up with some pynfs testing:

    [  123.609992] nfsd: non-standard errno: -7

...and -7 is -E2BIG. I think what happened is that XFS returned -E2BIG
due to some xattr operations with the ACL10 pynfs TEST (I guess it has
limited xattr size?).

Add a better mapping for that error since it's possible that we'll need
it. How about we convert it to NFSERR_FBIG? As Bruce points out, they
both have "BIG" in the name so it must be good.

Also, turn the printk in this function into a WARN() so that we can get
a bit more information about situations that don't have proper mappings.
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsproc.c

@@ -717,6 +717,7 @@ nfserrno (int errno)
 		{ nfserr_noent, -ENOENT },
 		{ nfserr_io, -EIO },
 		{ nfserr_nxio, -ENXIO },
+		{ nfserr_fbig, -E2BIG },
 		{ nfserr_acces, -EACCES },
 		{ nfserr_exist, -EEXIST },
 		{ nfserr_xdev, -EXDEV },
@@ -751,7 +752,7 @@ nfserrno (int errno)
 		if (nfs_errtbl[i].syserr == errno)
 			return nfs_errtbl[i].nfserr;
 	}
-	printk (KERN_INFO "nfsd: non-standard errno: %d\n", errno);
+	WARN(1, "nfsd: non-standard errno: %d\n", errno);
 	return nfserr_io;
 }