configure: don't use recvmmsg() on FreeBSD

Don't try recvmmsg() on FreeBSD, at least for now. It is broken on
FreeBSD 11.0 and it's just a wrapper around recvmsg().

configure

@@ -219,6 +219,7 @@ try_lockmem=0
 feat_asyncdns=1
 feat_forcednsretry=1
 try_clock_gettime=1
+try_recvmmsg=1
 feat_timestamping=1
 try_timestamping=0
 feat_ntp_signd=0
@@ -400,6 +401,9 @@ case $OPERATINGSYSTEM in
         echo "Configuring for " $SYSTEM
     ;;
     FreeBSD)
+        # recvmmsg() seems to be broken on FreeBSD 11.0 and it's just
+        # a wrapper around recvmsg()
+        try_recvmmsg=0
         EXTRA_OBJECTS="sys_generic.o sys_netbsd.o sys_timex.o"
         add_def FREEBSD
         if [ $feat_droproot = "1" ]; then
@@ -629,6 +633,7 @@ fi
 RECVMMSG_CODE='
   struct mmsghdr hdr;
   return !recvmmsg(0, &hdr, 1, MSG_DONTWAIT, 0);'
+if [ $try_recvmmsg = "1" ]; then
   if test_code 'recvmmsg()' 'sys/socket.h' '' "$EXTRA_LIBS" "$RECVMMSG_CODE"; then
     add_def HAVE_RECVMMSG
   else
@@ -639,6 +644,7 @@ else
       add_def HAVE_RECVMMSG
     fi
   fi
+fi
 
 if [ $feat_timestamping = "1" ] && [ $try_timestamping = "1" ] &&
   test_code 'SW/HW timestamping' 'sys/types.h sys/socket.h linux/net_tstamp.h