capability-util: introduce capability_get() and use it in have_effective_cap()

capability_get() is a wrapper of capget() syscall and converts its
result to CapabilityQuintet.

This also introduce have_inheritable_cap(), which is similar to
have_effective_cap(). It is currently unused, but will be used later.

src/basic/capability-util.h

@@ -43,8 +43,11 @@ static inline bool capability_is_set(uint64_t v) {
         return v != CAP_MASK_UNSET;
 }
 
+int capability_get(CapabilityQuintet *ret);
+
 unsigned cap_last_cap(void);
-int have_effective_cap(int value);
+int have_effective_cap(unsigned cap);
+int have_inheritable_cap(unsigned cap);
 int capability_gain_cap_setpcap(cap_t *ret_before_caps);
 int capability_bounding_set_drop(uint64_t keep, bool right_now);
 int capability_bounding_set_drop_usermode(uint64_t keep);