libcasper: Use __VA_ARGS__ for function-like macros

cap_net.h uses "#define cap_f(chan, a) f(a)" to call the conventional
service function with the first argument of cap_f() dropped for
compatibility with the environment where the casper service is
unavailable.  However, this function-like macro does not work when the
arguments contains C99 compound literals, such as f(chan, (int[]){1,2,3}).
The following is a typical example:

    error = cap_getaddrinfo(capnet, "192.168.0.1", "100",
        &(struct addrinfo){
            .ai_family = AF_INET,
            .ai_flags = AI_NUMERICHOST
    }, &res);

Using cap_f(chan, ...) and __VA_ARGS__ in C99 seems a reasonable solution
for this problem.  While there is a workaround using parenthesis around
the compound literal like f(chan, ((int[]){1,2,3})), it is not intuitive
and the above example works when the cap_net is available and f() is
defined as a function.

A possible moot point is that __VA_ARGS__ cannot control how many
arguments are passed at the macro level, and "chan" is not protected.
However, "chan" is less likely to be written in compound literal, and
the function prototype should check the remaining arguments.

Reviewed by:	oshogbo
Differential Revision:	https://reviews.freebsd.org/D45858

lib/libcasper/services/cap_net/cap_net.h

@@ -93,18 +93,14 @@ struct hostent *cap_gethostbyaddr(cap_channel_t *chan, const void *addr,
     socklen_t len, int af);
 #else
 /* Capability functions. */
-#define cap_bind(chan, s, addr, addrlen)					\
-	bind(s, addr, addrlen)
-#define cap_connect(chan, s, name, namelen)					\
-	connect(s, name, namelen)
-#define	cap_getaddrinfo(chan, hostname, servname, hints, res)			\
-	getaddrinfo(hostname, servname, hints, res)
-#define	cap_getnameinfo(chan, sa, salen, host, hostlen, serv, servlen, flags)	\
-	getnameinfo(sa, salen, host, hostlen, serv, servlen, flags)
+#define	cap_bind(chan, ...)	bind(__VA_ARGS__)
+#define	cap_connect(chan, ...)	connect(__VA_ARGS__)
+#define	cap_getaddrinfo(chan, ...)	getaddrinfo(__VA_ARGS__)
+#define	cap_getnameinfo(chan, ...)	getnameinfo(__VA_ARGS__)
 
 /* Limit functions. */
-#define cap_net_limit_init(chan, mode)	((cap_net_limit_t *)malloc(8))
-#define cap_net_free(limit)		free(limit)
+#define cap_net_limit_init(chan, ...)	((cap_net_limit_t *)malloc(8))
+#define cap_net_free(...)		free(__VA_ARGS__)
 static inline int
 cap_net_limit(cap_net_limit_t *limit)
 {
@@ -155,9 +151,9 @@ cap_net_limit_bind(cap_net_limit_t *limit,
 }
 
 /* Deprecated functions. */
-#define	cap_gethostbyname(chan, name)		 gethostbyname(name)
-#define	cap_gethostbyname2(chan, name, type)	 gethostbyname2(name, type)
-#define	cap_gethostbyaddr(chan, addr, len, type) gethostbyaddr(addr, len, type)
+#define	cap_gethostbyname(chan, ...)	gethostbyname(__VA_ARGS__)
+#define	cap_gethostbyname2(chan, ...)	gethostbyname2(__VA_ARGS__)
+#define	cap_gethostbyaddr(chan, ...)	gethostbyaddr(__VA_ARGS__)
 #endif
 
 #endif	/* !_CAP_NETWORK_H_ */