[IPV4]: Explicitly call fib_get_table() in fib_frontend.c

In case the "multiple tables" config option is y, the ip_fib_local_table
is not a variable, but a macro, that calls fib_get_table(RT_TABLE_LOCAL).

Some code uses this "variable" *3* times in one place, thus implicitly
making 3 calls. Fix it.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>