mnl: name is ignored when deleting a table

mnl: name is ignored when deleting a table

nlt is reallocated, leaking first allocation and also removing
the table name/handle that was set on nlt object.

Add a test case for this as well, the batch is supposed to fail
when trying to delete a non-existant table, rather than wiping
all tables in the same address family.

Fixes: 12c362e2214a0 ("mnl: remove alloc_nftnl_table()")
Reported-by:  Mikhail Morfikov <mmorfikov@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>