drivers: slip: Consistently log pkt/buf allocation failures

There are 3 cases of possible allocation failures, only 1 of them
was logged. Now, all the cases are logged: 1) failure to allocate
net_pkt; 2) failure to allocate very first net_buf for it; 3)
failure to allocate additional net_buf for it (this latter was
the only one logged previously).

Signed-off-by: Paul Sokolovsky <[email protected]>

drivers/slip/slip.c

@@ -309,11 +309,15 @@ static inline int slip_input_byte(struct slip_context *slip,
 
 			slip->rx = net_pkt_get_reserve_rx(0, K_NO_WAIT);
 			if (!slip->rx) {
+				SYS_LOG_ERR("[%p] cannot allocate pkt",
+					    slip);
 				return 0;
 			}
 
 			slip->last = net_pkt_get_frag(slip->rx, K_NO_WAIT);
 			if (!slip->last) {
+				SYS_LOG_ERR("[%p] cannot allocate 1st data frag",
+					    slip);
 				net_pkt_unref(slip->rx);
 				slip->rx = NULL;
 				return 0;
@@ -340,7 +344,7 @@ static inline int slip_input_byte(struct slip_context *slip,
 
 		frag = net_pkt_get_reserve_rx_data(0, K_NO_WAIT);
 		if (!frag) {
-			SYS_LOG_ERR("[%p] cannot allocate data fragment",
+			SYS_LOG_ERR("[%p] cannot allocate next data frag",
 				    slip);
 			net_pkt_unref(slip->rx);
 			slip->rx = NULL;