busybox: adjust nommu swaponoff handling for busybox 1.26.0+

Fixes:
http://autobuild.buildroot.net/results/dfe/dfec2c0626ab087325fd869bcbe0b9dc354d788c/

Busybox 1.26.0 gained separate config options for swapon / swapoff:

commit f417ffd88f194bbfd18605882ee242190c1bab34
Author: Denys Vlasenko <vda.linux@googlemail.com>
Date:   Mon Nov 14 17:30:50 2016 +0100

    Make swapon and swapoff individually selectable.

    For example, without swapoff, code shrinks by 277 bytes.

    Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

So adjust busybox.config and the logic to disable these applets for nommu
builds for the new names.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/busybox/busybox.config

@@ -633,9 +633,10 @@ CONFIG_READPROFILE=y
 # CONFIG_RTCWAKE is not set
 # CONFIG_SCRIPT is not set
 # CONFIG_SCRIPTREPLAY is not set
-CONFIG_SWAPONOFF=y
+CONFIG_SWAPON=y
 # CONFIG_FEATURE_SWAPON_DISCARD is not set
 # CONFIG_FEATURE_SWAPON_PRI is not set
+CONFIG_SWAPOFF=y
 CONFIG_SWITCH_ROOT=y
 CONFIG_UMOUNT=y
 CONFIG_FEATURE_UMOUNT_ALL=y

package/busybox/busybox.mk

@@ -96,7 +96,8 @@ endef
 else
 define BUSYBOX_SET_MMU
 	$(call KCONFIG_ENABLE_OPT,CONFIG_NOMMU,$(BUSYBOX_BUILD_CONFIG))
-	$(call KCONFIG_DISABLE_OPT,CONFIG_SWAPONOFF,$(BUSYBOX_BUILD_CONFIG))
+	$(call KCONFIG_DISABLE_OPT,CONFIG_SWAPON,$(BUSYBOX_BUILD_CONFIG))
+	$(call KCONFIG_DISABLE_OPT,CONFIG_SWAPOFF,$(BUSYBOX_BUILD_CONFIG))
 	$(call KCONFIG_DISABLE_OPT,CONFIG_ASH,$(BUSYBOX_BUILD_CONFIG))
 	$(call KCONFIG_ENABLE_OPT,CONFIG_HUSH,$(BUSYBOX_BUILD_CONFIG))
 	$(call KCONFIG_ENABLE_OPT,CONFIG_HUSH_BASH_COMPAT,$(BUSYBOX_BUILD_CONFIG))