xfrm: make xfrm_algo.c a module

By making this a standalone config option (auto-selected as needed),
selecting CRYPTO from here rather than from XFRM (which is boolean)
allows the core crypto code to become a module again even when XFRM=y.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index d183262..2c8febd 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -312,7 +312,7 @@
 
 config INET_AH
 	tristate "IP: AH transformation"
-	select XFRM
+	select XFRM_ALGO
 	select CRYPTO
 	select CRYPTO_HMAC
 	select CRYPTO_MD5
@@ -324,7 +324,7 @@
 
 config INET_ESP
 	tristate "IP: ESP transformation"
-	select XFRM
+	select XFRM_ALGO
 	select CRYPTO
 	select CRYPTO_AUTHENC
 	select CRYPTO_HMAC