net/sfc/base: move Tx descs number check to generic place
net/sfc/base: move Tx descs number check to generic place

Now we have min/max limits in NIC config, so we can do check against
min/max in a generic place instead of NIC family specific functions.
Check that the descriptors number is a power of 2 is also can be made
common. It removes code duplication and makes NIC family
specific functions a bit shorter.

Signed-off-by: Igor Romanov <945ea196dab32ad63762a1b623439a95515e898a@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <ac94ab2a8fe9a9a087f6e24dcbc16626b52c07e8@solarflare.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk