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>

net/ipv6/Kconfig

@@ -69,7 +69,7 @@ config IPV6_OPTIMISTIC_DAD
 
 config INET6_AH
 	tristate "IPv6: AH transformation"
-	select XFRM
+	select XFRM_ALGO
 	select CRYPTO
 	select CRYPTO_HMAC
 	select CRYPTO_MD5
@@ -81,7 +81,7 @@ config INET6_AH
 
 config INET6_ESP
 	tristate "IPv6: ESP transformation"
-	select XFRM
+	select XFRM_ALGO
 	select CRYPTO
 	select CRYPTO_AUTHENC
 	select CRYPTO_HMAC