fix(uavcan): Change SocketCAN return code handling

Don't forward posix return codes and parse errno instead so api knows
it neeeds to do a retry instead of a discard

Author: PetervdPerk-NXP

src/drivers/uavcan/uavcan_drivers/socketcan/driver/src/socketcan.cpp

@@ -200,7 +200,11 @@ uavcan::int16_t CanIface::send(const uavcan::CanFrame &frame, uavcan::MonotonicT
 		return 1;
 
 	} else {
-		return res;
+		if (errno == ENOBUFS || errno == EAGAIN || errno == EWOULDBLOCK) {
+			return 0; // Transmit queue is full, retry
+		}
+
+		return -1;
 	}
 }
 
@@ -210,7 +214,11 @@ uavcan::int16_t CanIface::receive(uavcan::CanFrame &out_frame, uavcan::Monotonic
 	int32_t result = recvmsg(_fd, &_recv_msg, MSG_DONTWAIT);
 
 	if (result < 0) {
-		return result;
+		if (errno == EAGAIN || errno == EWOULDBLOCK) {
+			return 0;
+		}
+
+		return -1;
 	}
 
 	/* Copy SocketCAN frame to CanardFrame */
@@ -220,7 +228,7 @@ uavcan::int16_t CanIface::receive(uavcan::CanFrame &out_frame, uavcan::Monotonic
 		out_frame.id = recv_frame->can_id;
 
 		if (recv_frame->len > CANFD_MAX_DLEN) {
-			return -EFAULT;
+			return -1;
 		}
 
 		out_frame.dlc = recv_frame->len;
@@ -231,7 +239,7 @@ uavcan::int16_t CanIface::receive(uavcan::CanFrame &out_frame, uavcan::Monotonic
 		out_frame.id = recv_frame->can_id;
 
 		if (recv_frame->can_dlc > CAN_MAX_DLEN) {
-			return -EFAULT;
+			return -1;
 		}
 
 		out_frame.dlc = recv_frame->can_dlc;
@@ -245,7 +253,7 @@ uavcan::int16_t CanIface::receive(uavcan::CanFrame &out_frame, uavcan::Monotonic
 		out_ts_monotonic = uavcan::MonotonicTime::fromUSec(tv->tv_sec * 1000000ULL + tv->tv_usec);
 	}
 
-	return result;
+	return 1;
 }