wireguard: do not use -O3

Apparently, various versions of gcc have O3-related miscompiles. Looking
at the difference between -O2 and -O3 for gcc 11 doesn't indicate
miscompiles, but the difference also doesn't seem so significant for
performance that it's worth risking.

Link: https://lore.kernel.org/lkml/CAHk-=[e-mail]/
Link: https://lore.kernel.org/lkml/[e-mail]/
Reported-by: Linus Torvalds <[e-mail]>
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Cc: [e-mail]
Signed-off-by: Jason A. Donenfeld <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/wireguard/Makefile

···
-ccflags-y := -O3
-ccflags-y += -D'pr_fmt(fmt)=KBUILD_MODNAME ": " fmt'
+ccflags-y := -D'pr_fmt(fmt)=KBUILD_MODNAME ": " fmt'
 ccflags-$(CONFIG_WIREGUARD_DEBUG) += -DDEBUG
 wireguard-y := main.o
 wireguard-y += noise.o