net: ipv6mr: fix unused variable warning with CONFIG_IPV6_PIMSM_V2=n

net/ipv6/ip6mr.c:1656:14: warning: unused variable 'do_wrmifwhole'

Move it to the CONFIG_IPV6_PIMSM_V2 scope where its used.

Fixes: 4b340a5a

 ("net: ip6mr: add support for passing full packet on wrong mif")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>