IB/core: Fix IPv6 netlink message size in ib_nl_ip_send_msg()

IB/core: Fix IPv6 netlink message size in ib_nl_ip_send_msg()

When resolving an RDMA-CM IPv6 address, ib_nl_ip_send_msg() sends a
netlink request to the userspace daemon to perform IP-to-GID
resolution in certain cases. The function allocates the netlink message
buffer using nla_total_size(sizeof(size)), which passes 8 bytes (the
size of size_t) instead of 16 bytes (the size of an IPv6 address).
This results in an 8-byte under-allocation.

This is currently masked by nlmsg_new() over-allocation of the skb
in its internal logic. However, the code remains incorrect.

Fix the issue by supplying the proper IPv6 address length to
nla_total_size().

Fixes: ae43f8286730 ("IB/core: Add IP to GID netlink offload")
Link: https://patch.msgid.link/r/20260427-security-bug-fixes-v3-3-4621fa52de0e@nvidia.com
Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Patrisious Haddad <phaddad@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>