net/hyperv: avoid uninitialized variable

The hdr_offset variable is only if we deal with a TCP or UDP packet,
but as the check surrounding its usage tests for skb_is_gso()
instead, the compiler has no idea if the variable is initialized
or not at that point:

drivers/net/hyperv/netvsc_drv.c: In function ‘netvsc_start_xmit’:
drivers/net/hyperv/netvsc_drv.c:494:42: error: ‘hdr_offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

This adds an additional check for the transport type, which
tells the compiler that this path cannot happen. Since the
get_net_transport_info() function should always be inlined
here, I don't expect this to result in additional runtime
checks.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -447,7 +447,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	 * Setup the sendside checksum offload only if this is not a
 	 * GSO packet.
 	 */
-	if (skb_is_gso(skb)) {
+	if ((net_trans_info & (INFO_TCP | INFO_UDP)) && skb_is_gso(skb)) {
 		struct ndis_tcp_lso_info *lso_info;
 
 		rndis_msg_size += NDIS_LSO_PPI_SIZE;