Bluetooth: ISO: zero the sockaddr before returning it in getname

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: ISO: zero the sockaddr before returning it in getname

iso_sock_getname() fills a struct sockaddr_iso in place and returns its
size without clearing it first, so bytes it does not write are copied to
user space from the kernel stack. The getsockname(2) and getpeername(2)
paths both run through do_getsockname(), which hands getname() an
uninitialized sockaddr_storage on the stack and copies back up to the
number of bytes getname() returns, so the driver has to initialize every
byte it accounts for.

Two ranges are left uninitialized:

- struct sockaddr_iso is 10 bytes but only 9 are written (family,
iso_bdaddr, iso_bdaddr_type), leaking the trailing pad byte on every
call.

- for a broadcast peer (BIS_LINK or PA_LINK) the returned length grows
by sizeof(struct sockaddr_iso_bc), but only bc_sid, bc_num_bis and
bc_bis are filled; bc_bdaddr and bc_bdaddr_type, the first 7 bytes of
that structure, are never written.

An unprivileged process can open a BTPROTO_ISO socket and reach the pad
leak with getsockname(); the broadcast leak needs an established BIS/PA
connection. l2cap and rfcomm already memset their sockaddr in getname
for the same reason; do the same here.