hostapd: MLO: Avoid use of mld_id as user configuration

hostapd: MLO: Avoid use of mld_id as user configuration

mld_id was provided as a user configuration to identify partner BSS
belonging to the same AP MLD. The same id is used at the protocol level
also to indicate the AP MLD ID of the MLD.

But, in general mld_id is a relative reference of the MLD where 0 is
used as the mld_id to represent the self MLD and in case of MLO MBSSID
mld_id of a non transmitted BSS affiliated to an AP MLD is based on the
relative BSS index of the non transmitted BSS from the transmitted BSS.
Hence mld_id need not be fetched from users, rather it can be identified
wherever required.

To verify if the partners belong to the same AP MLD the interface name
can be checked, since all link BSS partners of the same AP MLD belong to
the same interface.

Hence, remove use of mld_id user config and instead introduce two
functions hostapd_is_ml_partner() and hostapd_get_mld_id(). The former
is used to verify whether partners belong to the same AP MLD and the
latter is used to get the MLD ID of the BSS.

Signed-off-by: Sriram R <quic_srirrama@quicinc.com>
Signed-off-by: Aditya Kumar Singh <quic_adisi@quicinc.com>