net: remove address space warnings in net/socket.c

Casts __kernel to __user pointer require __force markup, so add it. Also
sock_get/setsockopt() takes @optval and/or @optlen arguments as user pointers
but were taking kernel pointers, use new variables 'uoptval' and/or 'uoptlen'
to fix it. These remove following warnings from sparse:

 net/socket.c:1922:46: warning: cast adds address space to expression (<asn:1>)
 net/socket.c:3061:61: warning: incorrect type in argument 4 (different address spaces)
 net/socket.c:3061:61:    expected char [noderef] <asn:1>*optval
 net/socket.c:3061:61:    got char *optval
 net/socket.c:3061:69: warning: incorrect type in argument 5 (different address spaces)
 net/socket.c:3061:69:    expected int [noderef] <asn:1>*optlen
 net/socket.c:3061:69:    got int *optlen
 net/socket.c:3063:67: warning: incorrect type in argument 4 (different address spaces)
 net/socket.c:3063:67:    expected char [noderef] <asn:1>*optval
 net/socket.c:3063:67:    got char *optval
 net/socket.c:3064:45: warning: incorrect type in argument 5 (different address spaces)
 net/socket.c:3064:45:    expected int [noderef] <asn:1>*optlen
 net/socket.c:3064:45:    got int *optlen
 net/socket.c:3078:61: warning: incorrect type in argument 4 (different address spaces)
 net/socket.c:3078:61:    expected char [noderef] <asn:1>*optval
 net/socket.c:3078:61:    got char *optval
 net/socket.c:3080:67: warning: incorrect type in argument 4 (different address spaces)
 net/socket.c:3080:67:    expected char [noderef] <asn:1>*optval
 net/socket.c:3080:67:    got char *optval

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>