net/qede: refactor Tx routine

Refactor TX routine such that TX BD updates can all be grouped together.
Based on the TX offloads requested the TX bitfields are calculated in
a temporary variable and TX BDs are updated at the end. This will minimize
the if checks also. This change is done to easily accommodate newer TX
offload operations in the future.

Signed-off-by: Harish Patil <harish.patil@cavium.com>