net/igb: support VF mailbox interrupt for link up/down

net/igb: support VF mailbox interrupt for link up/down

When using kernel PF and DPDK VF, when the PF driver finds the link
state changes, up -> down or down -> up, the driver will send a
message to VF by mailbox. This link state change may be
triggered by PHY disconnection/reconnection, user config change
like *ifconfig down/up* or interface parameter, like MTU change.

This patch enables the support of the mailbox interrupt,
so VF driver can receive the message for link up/down.
After VF receives this message, VF port need to be reset to
recover. This needs to be handled by the application so this patch
allows the app to register a reset callback so it can reset the VF port.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>