[release] Update version to 0.9.7+ post release

src/Makefile

 VERSION_MAJOR	= 0
 VERSION_MINOR	= 9
 VERSION_PATCH	= 7
-EXTRAVERSION	=
+EXTRAVERSION	= +
 MM_VERSION	= $(VERSION_MAJOR).$(VERSION_MINOR)
 VERSION		= $(MM_VERSION).$(VERSION_PATCH)$(EXTRAVERSION)
 CFLAGS		+= -DVERSION_MAJOR=$(VERSION_MAJOR) \