net: libwx: move rss_field to struct wx

For global RSS and multiple RSS scheme, the RSS type fields are defined
identically in the registers. So they can be defined as the macros
WX_RSS_FIELD_* to cleanup the codes. And to prepare for the RXFH support
in the next patch, move the rss_field to struct wx.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Link: https://patch.msgid.link/20250926023843.34340-3-jiawenwu@trustnetic.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>