Remove iptables rule for SCTP checksum fixup

[robmry]

Description

@akerouanton noted in #47871 (comment) that this code for SCTP checksum fixup can now be removed ...

moby/libnetwork/drivers/bridge/port_mapping_linux.go

Lines 542 to 560 in 8c2e4ca

	if b.Proto == types.SCTP {
	// Linux kernel v4.9 and below enables NETIF_F_SCTP_CRC for veth by
	// the following commit.
	// This introduces a problem when combined with a physical NIC without
	// NETIF_F_SCTP_CRC. As for a workaround, here we add an iptables entry
	// to fill the checksum.
	//
	// https://github.com/torvalds/linux/commit/c80fafbbb59ef9924962f83aac85531039395b18
	args = []string{
	"-p", b.Proto.String(),
	"--sport", strconv.Itoa(int(b.Port)),
	"-j", "CHECKSUM",
	"--checksum-fill",
	}
	rule := iptRule{ipv: ipv, table: iptables.Mangle, chain: "POSTROUTING", args: args}
	if err := programChainRule(rule, "MASQUERADE", enable); err != nil {
	return err
	}
	}

[Hoernchen]

It's quite the coincidence that I ended up finding this ticket, because my Issue is that this specific rule basically prevents using the same sctp port for local (docker nw) and remote (->reachable via physical nw if) clients at the same time, the sctp conn for local clients basically times out after INIT/INIT_ACK

This specifically breaks having both remote and local "sw only/zmq" enbs at the same time with the https://github.com/herlesupreeth/docker_open5gs setup.