qca_wlan_vendor_attr_roam_subcmd is an enum associated with the
attribute QCA_WLAN_VENDOR_ATTR_ROAMING_SUBCMD. It represents
different sub command values and these are not the attributes.
Hence, rename the enum to qca_wlan_vendor_roaming_subcmd.
Accordingly, the members of this enum are also renamed to
suite the usage.
Change-Id: Idbc80bf084ff293402fa2de368bc91b4fc659f01
CRs-Fixed: 2508204
30c93402ec