ndisc6: needs mmu

Fix below build error if !BR2_USE_MMU:

tcpspray.o: In function `tcpspray':
tcpspray.c:(.text+0x4a8): undefined reference to `fork'
collect2: ld returned 1 exit status
make[3]: *** [tcpspray] Error 1

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/ndisc6/Config.in

@@ -4,6 +4,7 @@ comment "ndisc6 requires a toolchain with IPv6 support"
 config BR2_PACKAGE_NDISC6
 	bool "ndisc6 tools"
 	depends on BR2_INET_IPV6
+	depends on BR2_USE_MMU # fork()
 	select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT_IF_LOCALE
 	help
 	  NDisc6 is a small collection of useful tools for IPv6 networking