iplink_can: add CAN XL TMS PWM configuration support

iplink_can: add CAN XL TMS PWM configuration support

This is the iproute2 counterpart of Linux kernel's commit 46552323fa67
("can: netlink: add PWM netlink interface").

When the TMS is switched on, the node uses PWM (Pulse Width Modulation)
during the data phase instead of the classic NRZ (Non Return to Zero)
encoding.

PWM is configured by three parameters:

  - PWMS: Pulse Width Modulation Short phase
  - PWML: Pulse Width Modulation Long phase
  - PWMO: Pulse Width Modulation Offset time

For each of these parameters, the CAN netlink interface defines three IFLA
symbols:

  - IFLA_CAN_PWM_PWM*_MIN: the minimum allowed value.
  - IFLA_CAN_PWM_PWM*_MAX: the maximum allowed value.
  - IFLA_CAN_PWM_PWM*: the runtime value.

This results in a total of nine IFLA symbols which are all nested in a
parent IFLA_CAN_XL_PWM symbol.

Add the "pwms", "pwml" and "pwmo" options to iplink_can which controls the
IFLA_CAN_PWM_PWM* runtime values.

Add the logic to query and print all those IFLA values. Update
print_usage() accordingly.

Example using the dummy_can driver:

  # modprobe dummy_can
  # ip link set can0 type can bitrate 1000000 xl on xbitrate 20000000 tms on
  $ ip --details link show can0
  5: can0: <NOARP> mtu 2060 qdisc noop state DOWN mode DEFAULT group default qlen 10
      link/can  promiscuity 0 allmulti 0 minmtu 76 maxmtu 2060
      can <XL,TMS> state STOPPED restart-ms 0
  	  bitrate 1000000 sample-point 0.750
  	  tq 6 prop-seg 59 phase-seg1 60 phase-seg2 40 sjw 20 brp 1
  	  dummy_can CC: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp_inc 1
  	  dummy_can FD: dtseg1 2..256 dtseg2 2..128 dsjw 1..128 dbrp 1..512 dbrp_inc 1
  	  tdco 0..127 tdcf 0..127
  	  xbitrate 20000000 xsample-point 0.625
  	  xtq 6 xprop-seg 2 xphase-seg1 2 xphase-seg2 3 xsjw 1 xbrp 1
  	  pwms 2 pwml 6 pwmo 0
  	  dummy_can XL: xtseg1 2..256 xtseg2 2..128 xsjw 1..128 xbrp 1..512 xbrp_inc 1
  	  xtdco 0..127 xtdcf 0..127
  	  pwms 1..8 pwml 2..24 pwmo 0..16
  	  clock 160000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 65536 tso_max_segs 65535 gro_max_size 65536 gso_ipv4_max_size 65536 gro_ipv4_max_size 65536

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>