net: stmmac: stmmac_is_jumbo_frm() returns boolean

net: stmmac: stmmac_is_jumbo_frm() returns boolean

stmmac_is_jumbo_frm() returns whether the driver considers the frame
size to be a jumbo frame, and thus returns 0/1 values. This is boolean,
so convert it to return a boolean and use false/true instead. Also
convert stmmac_xmit()'s is_jumbo to be bool, which causes several
variables to be repositioned to keep it in reverse Christmas-tree
order.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/E1vLIWW-0000000Ewkl-21Ia@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>