TWT HDD callbacks are registered dynamically when each TWT
command is received from userspace and unregistered while
sending response. This design was in place considering the
existing TWT commands are synchronous and multiple back to
back TWT commands will not be received. But now the TWT
commands from userspace can be received asynchronously.
So register the TWT callbacks statically during start modules in
wlan_hdd_twt_init().
Change-Id: I7dd9333c330a90fca421a2cc2574b2db76536e96
CRs-Fixed: 2830644
52adb4d599