isdn: Fix a sleep-in-atomic bug

The driver may sleep under a spin lock, the function call path is:
isdn_ppp_mp_receive (acquire the lock)
  isdn_ppp_mp_reassembly
    isdn_ppp_push_higher
      isdn_ppp_decompress
        isdn_ppp_ccp_reset_trans
          isdn_ppp_ccp_reset_alloc_state
            kzalloc(GFP_KERNEL) --> may sleep

To fixed it, the "GFP_KERNEL" is replaced with "GFP_ATOMIC".
Signed-off-by: NJia-Ju Bai <baijiaju1990@163.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/i4l/isdn_ppp.c

@@ -2364,7 +2364,7 @@ static struct ippp_ccp_reset_state *isdn_ppp_ccp_reset_alloc_state(struct ippp_s
 		       id);
 		return NULL;
 	} else {
-		rs = kzalloc(sizeof(struct ippp_ccp_reset_state), GFP_KERNEL);
+		rs = kzalloc(sizeof(struct ippp_ccp_reset_state), GFP_ATOMIC);
 		if (!rs)
 			return NULL;
 		rs->state = CCPResetIdle;