AP MLD: Introduce MLD level control interface socket

AP MLD: Introduce MLD level control interface socket

With MLO, each link have socket created with "<ifname>_link<link id>"
under the control interface directory.

Introduce a MLD level socket "<ifname>" as well under the same control
interface directory. This socket can be used to pass the command to its
partner links directly instead of using the link level socket. Link ID
needs to be passed with the command in a prefix way. If no Link ID is
provided the first link ID is selected.

The structure of the command is -
 "LINKID <link id> <COMMAND APPLICABALE FOR THE LINK>"

Directory looks something like this -
  $ ls /var/run/hostapd/
    wlan0
    wlan0_link0
    wlan0_link1

wlan0 here is the MLD level socket. Rest are each link level sockets.

This also helps to maintain backwards compatibility with applications
which looks for <ifname> under the control interface directory.

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