Currently, one can acquire a bitmask of supported modes of operation by using the GetCmdMapped function:

e, err := ethtool.NewEthtool()
if err != nil {
	panic(err.Error())
}
defer e.Close()
cmdGet, err := e.CmdGetMapped(*name)
if err != nil {
	panic(err.Error())
}
fmt.Printf("cmd get: %+d\n", cmdGet["Supported"])

Unfortunately, there is no information on what the individual bits mean.

In this PR, I added the names of some supported capabilities (which I got from here: https://github.com/lyonel/lshw/blob/fdab06ac0b190ea0aa02cd468f904ed69ce0d9f1/src/core/network.cc#L113). This enables users of this library to seamlessly check, which capacities the interface in question supports.

closes #46