cifs: hide unused functions

The newly added SMB2+ attribute support causes unused function
warnings when CONFIG_CIFS_XATTR is disabled:

fs/cifs/smb2ops.c:563:1: error: 'smb2_set_ea' defined but not used [-Werror=unused-function]
 smb2_set_ea(const unsigned int xid, struct cifs_tcon *tcon,
fs/cifs/smb2ops.c:513:1: error: 'smb2_query_eas' defined but not used [-Werror=unused-function]
 smb2_query_eas(const unsigned int xid, struct cifs_tcon *tcon,

This adds another #ifdef around the affected functions.

Fixes: 5517554e ("cifs: Add support for writing attributes on SMB2+")
Fixes: 95907fea ("cifs: Add support for reading attributes on SMB2+")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Steve French <smfrench@gmail.com>