af_iucv: Move sockaddr length checks to before accessing sa_family in bind and connect handlers

Verify that the caller-provided sockaddr structure is large enough to
contain the sa_family field, before accessing it in bind() and connect()
handlers of the AF_IUCV socket. Since neither syscall enforces a minimum
size of the corresponding memory region, very short sockaddrs (zero or
one byte long) result in operating on uninitialized memory while
referencing .sa_family.

Fixes: 52a82e23

 ("af_iucv: Validate socket address length in iucv_sock_bind()")
Signed-off-by: Mateusz Jurczyk <mjurczyk@google.com>
[jwi: removed unneeded null-check for addr]
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>