net/socket: fix type in assignment and trim long line

The commit ffb07550 ("copy_msghdr_from_user(): get rid of
field-by-field copyin") introduce a new sparse warning:

net/socket.c:1919:27: warning: incorrect type in assignment (different address spaces)
net/socket.c:1919:27:    expected void *msg_control
net/socket.c:1919:27:    got void [noderef] <asn:1>*[addressable] msg_control

and a line above 80 chars, let's fix them

Fixes: ffb07550 ("copy_msghdr_from_user(): get rid of field-by-field copyin")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>