add -D (don't fragment) to ping6

[David Gwynne]

this brings -D over to ping6.

ok?

Index: ping.8
===================================================================
RCS file: /cvs/src/sbin/ping/ping.8,v
retrieving revision 1.60
diff -u -p -r1.60 ping.8
--- ping.8      10 Nov 2018 05:03:23 -0000      1.60
+++ ping.8      10 Nov 2018 05:25:30 -0000
@@ -79,7 +79,7 @@
 .Op Fl w Ar maxwait
 .Ar host
 .Nm ping6
-.Op Fl dEefHLmnqv
+.Op Fl DdEefHLmnqv
 .Op Fl c Ar count
 .Op Fl h Ar hoplimit
 .Op Fl I Ar sourceaddr
@@ -116,10 +116,10 @@ If
 .Ar count
 is 0, send an unlimited number of packets.
 .It Fl D
-.Pq IPv4 only
+Don't fragment.
 Set the
 .Dv Don't Fragment
-bit.
+bit on IPv4 frames, or disable fragmentation of transmitted IPv6 packets.
 .It Fl d
 Set the
 .Dv SO_DEBUG
Index: ping.c
===================================================================
RCS file: /cvs/src/sbin/ping/ping.c,v
retrieving revision 1.231
diff -u -p -r1.231 ping.c
--- ping.c      10 Nov 2018 05:03:23 -0000      1.231
+++ ping.c      10 Nov 2018 05:25:31 -0000
@@ -291,7 +291,7 @@ main(int argc, char *argv[])
        preload = 0;
        datap = &outpack[ECHOLEN + ECHOTMLEN];
        while ((ch = getopt(argc, argv, v6flag ?
-           "c:dEefHh:I:i:Ll:mNnp:qS:s:T:V:vw:" :
+           "c:DdEefHh:I:i:Ll:mNnp:qS:s:T:V:vw:" :
            "DEI:LRS:c:defHi:l:np:qs:T:t:V:vw:")) != -1) {
                switch(ch) {
                case 'c':
@@ -681,6 +681,13 @@ main(int argc, char *argv[])
                                warn("setsockopt(IPV6_TVAL)"); /* XXX err? */
                }
 
+               if (df) {
+                       optval = 1;
+                       if (setsockopt(s, IPPROTO_IPV6, IPV6_DONTFRAG,
+                           &optval, (socklen_t)sizeof(optval)) < 0)
+                               warn("setsockopt(IPV6_DONTFRAG"); /* err? */
+               }
+
                optval = 1;
                if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVPKTINFO, &optval,
                    (socklen_t)sizeof(optval)) < 0)
@@ -2166,7 +2173,7 @@ usage(void)
 {
        if (v6flag) {
                fprintf(stderr,
-                   "usage: ping6 [-dEefHLmnqv] [-c count] [-h hoplimit] "
+                   "usage: ping6 [-DdEefHLmnqv] [-c count] [-h hoplimit] "
                    "[-I sourceaddr]\n\t[-i wait] [-l preload] [-p pattern] "
                    "[-s packetsize] [-T toskeyword]\n\t"
                    "[-V rtable] [-w maxwait] host\n");