More tests

protocols/isis/packet/csnp.go

protocols/isis/packet/decoder.go

protocols/isis/packet/header.go

protocols/isis/packet/header_test.go

protocols/isis/packet/hello.go

protocols/isis/packet/hello_test.go

protocols/isis/packet/isis.go

protocols/isis/packet/lsp.go

protocols/isis/packet/lsp_entry.go

protocols/isis/packet/psnp.go

protocols/isis/packet/tlv.go

protocols/isis/packet/tlv_checksum.go

protocols/isis/packet/tlv_dynamic_hostname.go

protocols/isis/packet/tlv_ip_interface_address.go

protocols/isis/packet/tlv_is_neighbors.go

protocols/isis/packet/tlv_p2p_adj_state.go

protocols/isis/packet/tlv_protocols_supported.go