MFC r331340, r331342, r331472, r332050, r333276, r333448:

r331340:
cxgbe(4): Tunnel congestion drops on a port should be cleared when the
stats for that port are cleared.

r331342:
cxgbe(4): Do not read MFG diags information from custom boards.

r331472:
cxgbe(4): Always initialize requested_speed to a valid value.

This fixes an avoidable EINVAL when the user tries to disable AN after
the port is initialized but l1cfg doesn't have a valid speed to use.

r332050:
cxgbe(4): Always display an error message if SIOCSIFFLAGS will leave
IFF_UP and IFF_DRV_RUNNING out of sync. ifhwioctl in the kernel pays no
attention to the return code from the driver ioctl during SIOCSIFFLAGS
so these messages are the only indication that the ioctl was called but
failed.

r333276:
cxgbe(4): Update all firmwares to 1.19.1.0.

r333448:
cxgbe(4): Disable write-combined doorbells by default.

This had been the default behavior but was changed accidentally as part
of the recent iw_cxgbe+OFED overhaul. Fix another bug in that change
while here: the global knob affects all the adapters in the system and
should be left alone by per-adapter code.

Approved by: re@ (marius@)
Sponsored by: Chelsio Communications