pim6d: Fix the Code for MLD in the show pim state command

pim6d: Fix the Code for MLD in the show pim state command

show ip pim state should show IGMP Report while
show ipv6 pim state should show MLD Report.

Output After Fix:
frr# do sh ip pim state
Codes: J -> Pim Join, I -> IGMP Report, S -> Source, * -> Inherited from (*,G), V -> VxLAN, M -> Muted
Active Source           Group            RPT  IIF               OIL

frr# do sh ipv6 pim state
Codes: J -> Pim Join, I -> MLD Report, S -> Source, * -> Inherited from (*,G), V -> VxLAN, M -> Muted
Active Source           Group            RPT  IIF               OIL

frr#

Issue: #11249

Signed-off-by: Mobashshera Rasool <mrasool@vmware.com>