ip: add missing space after 'external' in detailed mode

ip: add missing space after 'external' in detailed mode

Add a missing space after the 'external' keyword in the detailed mode
of tunnel links output:

 # ip -d link
 79: geneve1: <BROADCAST,MULTICAST> mtu 65465 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ether da:e9:e4:2b:f9:d4 brd ff:ff:ff:ff:ff:ff promiscuity 0 minmtu 68 maxmtu 65465
     geneve externaladdrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
 80: vxlan1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ether 7a:a8:19:07:da:01 brd ff:ff:ff:ff:ff:ff promiscuity 0 minmtu 68 maxmtu 65535
     vxlan externaladdrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
 84: gre1@NONE: <NOARP> mtu 1476 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/none 00:00:00:00 brd 00:00:00:00 promiscuity 0 minmtu 0 maxmtu 0
     gre externaladdrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
 87: ip6gre1@NONE: <NOARP> mtu 1448 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/gre6 :: brd :: promiscuity 0 minmtu 0 maxmtu 0
     ip6gre externaladdrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
 88: ip6tnl1@NONE: <NOARP> mtu 1452 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/tunnel6 :: brd :: promiscuity 0 minmtu 68 maxmtu 65407
     ip6tnl externaladdrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
 90: ipip1@NONE: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ipip 0.0.0.0 brd 0.0.0.0 promiscuity 0 minmtu 0 maxmtu 0
     ipip externaladdrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

Fixes: 00ff4b8e31af ("ip/tunnel: Be consistent when printing tunnel collect metadata")
Reviewed-and-tested-by: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Beniamino Galvani <bgalvani@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>