packet.7: Fix include file

It looks like most of the socket options from this man pages
are not defined in <netpacket/packet.h>. They are defined in
<linux/if_packet.h> so we should include that one.

Note from mtk: it looks like <netpacket/packet.h> was based
on some ancient version of <linux/if_packet.h> that has not
been updated. Since linux/if_packet.h is under the "uapi" tree
the proposed patch seems the bext fix.

Signed-off-by: Sorin Dumitru <sdumitru@ixiacom.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/packet.7

@@ -16,7 +16,7 @@ packet \- packet interface on device level
 .nf
 .B #include <sys/socket.h>
 .br
-.B #include <netpacket/packet.h>
+.B #include <linux/if_packet.h>
 .br
 .B #include <net/ethernet.h>     /* the L2 protocols */
 .sp
@@ -535,18 +535,6 @@ is a new feature in Linux 2.2.
 Earlier Linux versions supported only
 .BR SOCK_PACKET .
 .PP
-The include file
-.I <netpacket/packet.h>
-is present since glibc 2.1.
-Older systems need:
-.sp
-.in +4n
-.nf
-#include <asm/types.h>
-#include <linux/if_packet.h>
-#include <linux/if_ether.h>  /* The L2 protocols */
-.fi
-.in
 .SH NOTES
 For portable programs it is suggested to use
 .B AF_PACKET