be2net: isolate TX workarounds not applicable to Skyhawk-R

Some of TX workarounds in be_xmit_workarounds() routine
are not applicable (and result in HW errors) to Skyhawk-R chip.
Isolate BE3-R/Lancer specific workarounds to a separate routine.

Signed-off-by: Vasundhara Volam <vasundhara.volam@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: Somnath Kotur <somnath.kotur@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>