Simplify the use of <sys/sockio.h>.

Simplify the use of <sys/sockio.h>.

In fad-gifc.c do not try including <sys/sockio.h>: the .c file is for
AIX 7 and HP-UX 11 only, and these OSes do not have the header, so the
guarded block is dead code.  Most other files that need the SIOCGIF*
macros are sufficiently OS-specific to know whether to include
<sys/sockio.h>, the only exception is pcap.c, which needs to compile on
all platforms.  Solve this by including <sys/sockio.h> on illumos, Haiku
and Solaris only.

These changes make HAVE_SYS_SOCKIO_H unused, so remove respective header
checks from Autoconf and CMake.  While at it, include <sys/ioctl.h> from
pcap-netmap.c for consistency.