key: fix setkey(8) policy set breakage

Steps to reproduce:

#/usr/sbin/setkey -f
flush;
spdflush;

add 192.168.0.42 192.168.0.1 ah 24500 -A hmac-md5 "1234567890123456";
add 192.168.0.42 192.168.0.1 esp 24501 -E 3des-cbc "123456789012123456789012";

spdadd 192.168.0.42 192.168.0.1 any -P out ipsec
esp/transport//require
ah/transport//require;

setkey: invalid keymsg length

Policy dump will bail out with the same message after that.

-recv(4, "\2\16\0\0\32\0\3\0\0\0\0\0\37\r\0\0\3\0\5\0\377 \0\0\2\0\0\0\300\250\0*\0"..., 32768, 0) = 208
+recv(4, "\2\16\0\0\36\0\3\0\0\0\0\0H\t\0\0\3\0\5\0\377 \0\0\2\0\0\0\300\250\0*\0"..., 32768, 0) = 208

Signed-off-by: Alexey Dobriyan <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/key/af_key.c

···
 			req_size += socklen * 2;
 		} else {
 			size -= 2*socklen;
-			socklen = 0;
 		}
 		rq = (void*)skb_put(skb, req_size);
 		pol->sadb_x_policy_len += req_size/8;