ip: Treat IPv4 segment's lowest address as unicast

mainline inclusion
from mainline-v5.14-rc1
commit 94c821c7
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9PX8J

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=94c821c74bf5fe0c25e09df5334a16f98608db90



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Treat only the highest, not the lowest, IPv4 address within a local
subnet as a broadcast address.

Signed-off-by: Seth David Schoen <schoen@loyalty.org>
Suggested-by: John Gilmore <gnu@toad.com>
Acked-by: Dave Taht <dave.taht@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Conflicts:
	net/ipv4/fib_frontend.c
[There is no conflict when cherry-picking. But we backport newer commit
0c51e12e causing the checkconflict CI fail.]
Signed-off-by: Liu Jian <liujian56@huawei.com>