ipvs: use explicitly signed chars

[ Upstream commit 5c26159c97b324dc5174a5713eafb8c855cf8106 ]

The `char` type with no explicit sign is sometimes signed and sometimes
unsigned. This code will break on platforms such as arm, where char is
unsigned. So mark it here as explicitly signed, so that the
todrop_counter decrement and subsequent comparison is correct.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>