Description of problem:
Getting a crash while i am running the test case tests/bugs/replicate/bug-1266876-allow-reset-brick-for-same-path.t


0x00007f38c9bf17d9 in glusterd_svcs_stop (volinfo=0x7f38bc01d9d0) at glusterd-svc-helper.c:90
#2  0x00007f38c9bf75d0 in glusterd_op_reset_brick (dict=dict@entry=0x7f38bc006108, rsp_dict=rsp_dict@entry=0x7f38bc00a838)
    at glusterd-reset-brick.c:329
#3  0x00007f38c9bd65cb in gd_mgmt_v3_commit_fn (op=op@entry=GD_OP_RESET_BRICK, dict=dict@entry=0x7f38bc006108, 
    op_errstr=op_errstr@entry=0x7f38b8405910, op_errno=op_errno@entry=0x7f38b840590c, rsp_dict=rsp_dict@entry=0x7f38bc00a838)
    at glusterd-mgmt.c:341
#4  0x00007f38c9bd99e6 in glusterd_mgmt_v3_commit (op=op@entry=GD_OP_RESET_BRICK, op_ctx=op_ctx@entry=0x7f38bc002ac8, 
    req_dict=0x7f38bc006108, op_errstr=op_errstr@entry=0x7f38b8405910, op_errno=op_errno@entry=0x7f38b840590c, 
    txn_generation=txn_generation@entry=0) at glusterd-mgmt.c:1577
#5  0x00007f38c9b932d1 in glusterd_mgmt_v3_initiate_replace_brick_cmd_phases (req=req@entry=0x7f38b80018b8, 
    op=op@entry=GD_OP_RESET_BRICK, dict=0x7f38bc002ac8) at glusterd-replace-brick.c:662
#6  0x00007f38c9b937ef in __glusterd_handle_replace_brick (req=req@entry=0x7f38b80018b8) at glusterd-replace-brick.c:147
#7  0x00007f38c9af72ee in glusterd_big_locked_handler (req=0x7f38b80018b8, 
    actor_fn=0x7f38c9b93310 <__glusterd_handle_replace_brick>) at glusterd-handler.c:79
#8  0x00007f38d723d6b0 in synctask_wrap () at syncop.c:272
#9  0x00007f38d5637010 in ?? () from /lib64/libc.so.6
#10 0x0000000000000000 in ?? ()

It is crashing in this function
ret = priv->nfs_svc.stop(&(priv->nfs_svc), SIGKILL);
    if (ret)
        goto out;
here nfs_svc is NULL because nfs_svc specific code executed only while we do pass gnfs to configure


Need to protect access to priv->nfs_svc members only if priv_nfs_svc != NULL