ixgbe/base: rework link speed branches
ixgbe/base: rework link speed branches

Use switch-case statement to replace if-else statement.

Signed-off-by: Changchun Ouyang <593bf1f161e79772915ea885e47cf0e95f4498c0@intel.com>
Acked-by: Jijiang Liu <10b95deab7df654d0c21c8c98b54c9a1ecf2a5c0@intel.com>

phermansson/dpdk,phermansson/dpdk,phermansson/dpdk,phermansson/dpdk