isisd: fix vty show isis metric

isisd: fix vty show isis metric

the vtysh command to set the isis metric on an interface
is 'isis metric level-1 X', but when showing the running
config we were displaying it as 'isis metric X level-1'.
This would confuse frr-reload.py when attempting to apply
a config file populated with the correct command; on the
other hand, using the show command format would return an
error when running vtysh -C on the file.

Fix this by making the show command return the same format
as the vtysh setting command.

Signed-off-by: Emanuele Di Pascale <emanuele@voltanet.io>