rcmd.3: SYNOPSIS: Use 'restrict' in prototypes

rcmd.3: SYNOPSIS: Use 'restrict' in prototypes

glibc uses 'restrict' in rcmd(), rcmd_af(), iruserok_af().
Let's use it here too.

.../glibc$ grep_glibc_prototype rcmd
resolv/netdb.h:449:
extern int rcmd (char **__restrict __ahost, unsigned short int __rport,
		 const char *__restrict __locuser,
		 const char *__restrict __remuser,
		 const char *__restrict __cmd, int *__restrict __fd2p);
.../glibc$ grep_glibc_prototype rcmd_af
resolv/netdb.h:461:
extern int rcmd_af (char **__restrict __ahost, unsigned short int __rport,
		    const char *__restrict __locuser,
		    const char *__restrict __remuser,
		    const char *__restrict __cmd, int *__restrict __fd2p,
		    sa_family_t __af);
.../glibc$ grep_glibc_prototype iruserok_af
resolv/netdb.h:537:
extern int iruserok_af (const void *__raddr, int __suser,
			const char *__remuser, const char *__locuser,
			sa_family_t __af);
.../glibc$

Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>