pimd: Introduce show command for protocol counters

pimd: Introduce show command for protocol counters

For all pim enabled interfaces and single pim enable interface command.
Clear command to clear protocol counters stats.

'show ip pim interface traffic {WORD} {json}'

'clear ip pim interface traffic'

Testing Done: bringup Pim configuration and form RPT and SPT and check
show ip pim interface traffic command output,
perform clear form of interface traffic command and
verified all counters reset via show form of command.
tor-21# show ip pim interface traffic swp2

Interface       HELLO            JOIN            PRUNE            REGISTER        REGISTER-STOP    ASSERT
                Rx/Tx            Rx/Tx           Rx/Tx            Rx/Tx             Rx/Tx           Rx/Tx
---------------------------------------------------------------------------------------------------------------
swp2             22/22             0/10            0/0             0/0             0/0             0/0

leaf-22# show ip pim interface traffic swp3

Interface       HELLO            JOIN            PRUNE            REGISTER        REGISTER-STOP    ASSERT
                Rx/Tx            Rx/Tx           Rx/Tx            Rx/Tx             Rx/Tx           Rx/Tx
---------------------------------------------------------------------------------------------------------------
swp3             23/22            10/0             0/0             0/0             0/0             0/0

spine-1#show ip pim interface traffic

Interface       HELLO            JOIN            PRUNE            REGISTER        REGISTER-STOP    ASSERT
                Rx/Tx            Rx/Tx           Rx/Tx            Rx/Tx             Rx/Tx           Rx/Tx
---------------------------------------------------------------------------------------------------------------
br1               0/1              0/0             0/0             0/0             0/0             0/0
lo                0/0              0/0             0/0             0/0             0/0             0/0
swp1              0/1              0/0             0/0             0/0             0/0             0/0
swp2              0/1              0/0             0/0             0/0             0/0             0/0

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>