wifi: ath12k: allocate new links in change_vif_links()

wifi: ath12k: allocate new links in change_vif_links()

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
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00130-QCAHKSWPL_SILICONZ-1.97421.5 # Nicolas Escande

Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Signed-off-by: Aditya Kumar Singh <aditya.kumar.singh@oss.qualcomm.com>
Tested-by: Nicolas Escande <nico.escande@gmail.com>
Link: https://patch.msgid.link/20250204-unlink_link_arvif_from_chanctx-v2-7-764fb5973c1a@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>