libsepol: add ebitmap iterator wrapper with startnode

Similar like ebitmap_for_each_bit() iterates over all bits of an ebitmap
add ebitmap_for_each_bit_starting() iterating over all bits starting
from a specific node and bit, which can be from an outer iteration.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
---
v2:
   * use _after suffix
   * reorder parameters

libsepol/include/sepol/policydb/ebitmap.h

@@ -80,6 +80,13 @@ static inline int ebitmap_node_get_bit(const ebitmap_node_t * n, unsigned int bi
 #define ebitmap_for_each_positive_bit(e, n, bit) \
 	ebitmap_for_each_bit(e, n, bit) if (ebitmap_node_get_bit(n, bit)) \
 
+#define ebitmap_for_each_bit_after(e, n, bit, startnode, startbit) \
+	n = startnode; \
+	for (bit = ebitmap_next(&n, startbit); bit < ebitmap_length(e); bit = ebitmap_next(&n, bit)) \
+
+#define ebitmap_for_each_positive_bit_after(e, n, bit, startnode, startbit) \
+	ebitmap_for_each_bit_after(e, n, bit, startnode, startbit) if (ebitmap_node_get_bit(n, bit)) \
+
 extern int ebitmap_cmp(const ebitmap_t * e1, const ebitmap_t * e2);
 extern int ebitmap_or(ebitmap_t * dst, const ebitmap_t * e1, const ebitmap_t * e2);
 extern int ebitmap_union(ebitmap_t * dst, const ebitmap_t * e1);