net: ipa: record the route table size in the IPA structure

The non-hashed routing tables for IPv4 and IPv6 will be the same
size.  And if supported, the hashed routing tables will be the same
size as the non-hashed tables.

Record the size (number of entries) of all routing tables in the IPA
structure.  For now, initialize this field using IPA_ROUTE_TABLE_MAX,
and just do so when the first route table is validated.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>