net: xfrm: fix old-style declaration

Modern C standards expect the '__inline__' keyword to come before the return
type in a declaration, and we get a couple of warnings for this with "make W=1"
in the xfrm{4,6}_policy.c files:

net/ipv6/xfrm6_policy.c:369:1: error: 'inline' is not at beginning of declaration [-Werror=old-style-declaration]
 static int inline xfrm6_net_sysctl_init(struct net *net)
net/ipv6/xfrm6_policy.c:374:1: error: 'inline' is not at beginning of declaration [-Werror=old-style-declaration]
 static void inline xfrm6_net_sysctl_exit(struct net *net)
net/ipv4/xfrm4_policy.c:339:1: error: 'inline' is not at beginning of declaration [-Werror=old-style-declaration]
 static int inline xfrm4_net_sysctl_init(struct net *net)
net/ipv4/xfrm4_policy.c:344:1: error: 'inline' is not at beginning of declaration [-Werror=old-style-declaration]
 static void inline xfrm4_net_sysctl_exit(struct net *net)

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>