Netmap contract update routine

[alexvanin]

All FrostFS contracts aside netmap have simple update routine which is defined in if isUpdate branch of _deploy function.
Netmap contract have mandatory system config update and it requires specific arguments format for update function.

frostfs-contract/netmap/netmap_contract.go

Lines 74 to 93 in 4f3c08f

	var args = data.(struct {
	notaryDisabled bool
	addrBalance interop.Hash160
	addrContainer interop.Hash160
	keys []interop.PublicKey
	config [][]byte
	version int
	})
	ln := len(args.config)
	if ln%2 != 0 {
	panic("bad configuration")
	}
	for i := 0; i < ln/2; i++ {
	key := args.config[i*2]
	val := args.config[i*2+1]
	setConfig(ctx, key, val)
	}

It looks to me as outdated code and it would be nice to have more flexibility in update arguments format for netmap contract. So my propose is to move if isUpdate branch before argument parsing and setConfig call.