NFSv4_2: SSC helper should use its own config.

Currently NFSv4_2 SSC helper, nfs_ssc, incorrectly uses GRACE_PERIOD
as its config. Fix by adding new config NFS_V4_2_SSC_HELPER which
depends on NFS_V4_2 and is automatically selected when NFSD_V4 is
enabled. Also removed the file name from a comment in nfs_ssc.c.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
diff --git a/fs/nfs_common/Makefile b/fs/nfs_common/Makefile
index fa82f5a..119c75a 100644
--- a/fs/nfs_common/Makefile
+++ b/fs/nfs_common/Makefile
@@ -7,4 +7,4 @@
 nfs_acl-objs := nfsacl.o
 
 obj-$(CONFIG_GRACE_PERIOD) += grace.o
-obj-$(CONFIG_GRACE_PERIOD) += nfs_ssc.o
+obj-$(CONFIG_NFS_V4_2_SSC_HELPER) += nfs_ssc.o