net: get rid of some pointless casts to sockaddr

The following 4 functions:
  move_addr_to_kernel
  move_addr_to_user
  verify_iovec
  verify_compat_iovec
are always effectively called with a sockaddr_storage.

Make this explicit by changing their signature.

This removes a large number of casts from sockaddr_storage to sockaddr.

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>