Currently, links in an interface are allocated during channel assignment
via assign_vif_chanctx(). Conversely, links are deleted during channel
unassignment via unassign_vif_chanctx(). However, deleting links during
channel unassignment does not comply with mac80211 link handling.
Therefore, this process should be managed within change_vif_links(). To
maintain symmetry, link addition should also be handled in
change_vif_links().
Hence, add changes to allocate link arvif in change_vif_links(). Creating
the link interface on firmware will still be done during channel
assignment.
And since link will be created but channel might not be assigned, there is
a need now to test is_created flag in ath12k_mac_mlo_get_vdev_args() before
accessing link_conf or else link bring up will fail.
A subsequent change will handle link removal part.
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00173-QCAHKSWPL_SILICONZ-1
Signed-off-by: Aditya Kumar Singh <aditya.kumar.singh@xxxxxxxxxxxxxxxx>