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