rndis_filter uses utf8s_to_utf16s() which is provided by setting
NLS, so select NLS to fix the build error:

ERROR: modpost: "utf8s_to_utf16s" [drivers/net/hyperv/hv_netvsc.ko] undefined!

Fixes: 1ce09e89 ("hyperv: Add support for setting MAC from within guests")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Simon Horman <horms@kernel.org> # build-tested
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20231130055853.19069-1-rdunlap@infradead.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>