net: stmmac: simplify GSO/TSO test in stmmac_xmit()

net: stmmac: simplify GSO/TSO test in stmmac_xmit()

The test in stmmac_xmit() to see whether we should pass the skbuff to
stmmac_tso_xmit() is more complex than it needs to be. This test can
be simplified by storing the mask of GSO types that we will pass, and
setting it according to the enabled features.

Note that "tso" is a mis-nomer since commit b776620651a1 ("net:
stmmac: Implement UDP Segmentation Offload"). Also note that this
commit controls both via the TSO feature. We preserve this behaviour
in this commit.

Also, this commit unconditionally accessed skb_shinfo(skb)->gso_type
for all frames, even when skb_is_gso() was false. This access is
eliminated.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1w7ptj-0000000Eatb-11zK@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>