xfrm: kconfig: make xfrm depend on inet

when CONFIG_INET is not enabled:
net/xfrm/xfrm_output.c: In function ‘xfrm4_tunnel_encap_add’:
net/xfrm/xfrm_output.c:234:2: error: implicit declaration of function ‘ip_select_ident’ [-Werror=implicit-function-declaration]
ip_select_ident(dev_net(dst->dev), skb, NULL);

XFRM only supports ipv4 and ipv6 so change dependency to INET and place
user-visible options (pfkey sockets, migrate support and the like)
under 'if INET' guard as well.

Fixes: 1de7083006 ("xfrm: remove output2 indirection from xfrm_mode")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/Kconfig

@@ -3,7 +3,7 @@
 #
 config XFRM
        bool
-       depends on NET
+       depends on INET
        select GRO_CELLS
        select SKB_EXTENSIONS
 
@@ -15,9 +15,9 @@ config XFRM_ALGO
 	select XFRM
 	select CRYPTO
 
+if INET
 config XFRM_USER
 	tristate "Transformation user configuration interface"
-	depends on INET
 	select XFRM_ALGO
 	---help---
 	  Support for Transformation(XFRM) user configuration interface
@@ -56,7 +56,7 @@ config XFRM_MIGRATE
 
 config XFRM_STATISTICS
 	bool "Transformation statistics"
-	depends on INET && XFRM && PROC_FS
+	depends on XFRM && PROC_FS
 	---help---
 	  This statistics is not a SNMP/MIB specification but shows
 	  statistics about transformation error (or almost error) factor
@@ -95,3 +95,5 @@ config NET_KEY_MIGRATE
 	  <draft-sugimoto-mip6-pfkey-migrate>.
 
 	  If unsure, say N.
+
+endif # INET