xfrm: interface: rename xfrm_interface.c to xfrm_interface_core.c

This change allows adding additional files to the xfrm_interface module.
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Link: https://lore.kernel.org/r/20221203084659.1837829-2-eyal.birger@gmail.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

net/xfrm/Makefile

@@ -3,6 +3,8 @@
 # Makefile for the XFRM subsystem.
 #
 
+xfrm_interface-$(CONFIG_XFRM_INTERFACE) += xfrm_interface_core.o
+
 obj-$(CONFIG_XFRM) := xfrm_policy.o xfrm_state.o xfrm_hash.o \
 		      xfrm_input.o xfrm_output.o \
 		      xfrm_sysctl.o xfrm_replay.o xfrm_device.o