MFC r199237, r199238, r199239, r199240, r200003

MFC r199237, r199238, r199239, r199240, r200003

r199237:
sc->rev and is_offload(sc) will always be 0 during probe.  Wait till
attach to get correct values.

r199238:
Make sure *some* edc is setup even for an unknown transceiver (assume
it is optical).

r199239:
The 10GBASE-T card should use an IPG of 1.  Also enable the check
for low power startup on this card.

r199240:
Don't disable the XGMAC's tx on ifconfig down.  It is unnecessary
and can cause false backpressure in the chip.  Fix a us/ms mixup
while here.

r200003:
T3 firmware 7.8.0 for cxgb(4)

git-svn-id: svn://svn.freebsd.org/base/stable/8@200175 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f