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/xfrm/Makefile

@@ -3,8 +3,9 @@
 #
 
 obj-$(CONFIG_XFRM) := xfrm_policy.o xfrm_state.o xfrm_hash.o \
-		      xfrm_input.o xfrm_output.o xfrm_algo.o \
+		      xfrm_input.o xfrm_output.o \
 		      xfrm_sysctl.o xfrm_replay.o
 obj-$(CONFIG_XFRM_STATISTICS) += xfrm_proc.o
+obj-$(CONFIG_XFRM_ALGO) += xfrm_algo.o
 obj-$(CONFIG_XFRM_USER) += xfrm_user.o
 obj-$(CONFIG_XFRM_IPCOMP) += xfrm_ipcomp.o