xfrm: remove input2 indirection from xfrm_mode

No external dependencies on any module, place this in the core.
Increase is about 1800 byte for xfrm_input.o.

The beet helpers get added to internal header, as they can be reused
from xfrm_output.c in the next patch (kernel contains several
copies of them in the xfrm{4,6}_mode_beet.c files).

Before:
   text    data     bss     dec filename
   5578     176    2364    8118 net/xfrm/xfrm_input.o
   1180      64       0    1244 net/ipv4/xfrm4_mode_beet.o
    171      40       0     211 net/ipv4/xfrm4_mode_transport.o
   1163      40       0    1203 net/ipv4/xfrm4_mode_tunnel.o
   1083      52       0    1135 net/ipv6/xfrm6_mode_beet.o
    172      40       0     212 net/ipv6/xfrm6_mode_ro.o
    172      40       0     212 net/ipv6/xfrm6_mode_transport.o
   1056      40       0    1096 net/ipv6/xfrm6_mode_tunnel.o

After:
   text    data     bss     dec filename
   7373     200    2364    9937 net/xfrm/xfrm_input.o
    587      44       0     631 net/ipv4/xfrm4_mode_beet.o
    171      32       0     203 net/ipv4/xfrm4_mode_transport.o
    649      32       0     681 net/ipv4/xfrm4_mode_tunnel.o
    625      44       0     669 net/ipv6/xfrm6_mode_beet.o
    172      32       0     204 net/ipv6/xfrm6_mode_ro.o
    172      32       0     204 net/ipv6/xfrm6_mode_transport.o
    599      32       0     631 net/ipv6/xfrm6_mode_tunnel.o

v2: pass inner_mode to xfrm_inner_mode_encap_remove to fix
    AF_UNSPEC selector breakage (bisected by Benedict Wong)

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/xfrm/xfrm_inout.h b/net/xfrm/xfrm_inout.h
new file mode 100644
index 0000000..c7b0318
--- /dev/null
+++ b/net/xfrm/xfrm_inout.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/ipv6.h>
+#include <net/dsfield.h>
+#include <net/xfrm.h>
+
+#ifndef XFRM_INOUT_H
+#define XFRM_INOUT_H 1
+
+static inline void xfrm6_beet_make_header(struct sk_buff *skb)
+{
+	struct ipv6hdr *iph = ipv6_hdr(skb);
+
+	iph->version = 6;
+
+	memcpy(iph->flow_lbl, XFRM_MODE_SKB_CB(skb)->flow_lbl,
+	       sizeof(iph->flow_lbl));
+	iph->nexthdr = XFRM_MODE_SKB_CB(skb)->protocol;
+
+	ipv6_change_dsfield(iph, 0, XFRM_MODE_SKB_CB(skb)->tos);
+	iph->hop_limit = XFRM_MODE_SKB_CB(skb)->ttl;
+}
+
+static inline void xfrm4_beet_make_header(struct sk_buff *skb)
+{
+	struct iphdr *iph = ip_hdr(skb);
+
+	iph->ihl = 5;
+	iph->version = 4;
+
+	iph->protocol = XFRM_MODE_SKB_CB(skb)->protocol;
+	iph->tos = XFRM_MODE_SKB_CB(skb)->tos;
+
+	iph->id = XFRM_MODE_SKB_CB(skb)->id;
+	iph->frag_off = XFRM_MODE_SKB_CB(skb)->frag_off;
+	iph->ttl = XFRM_MODE_SKB_CB(skb)->ttl;
+}
+
+#endif