igb: Always copy ethernet header

igb: Always copy ethernet header

igb_receive_internal() used to check the iov length to determine
copy the iovs to a contiguous buffer, but the check is flawed in two
ways:
- It does not ensure that iovcnt > 0.
- It does not take virtio-net header into consideration.

The size of this copy is just 22 octets, which can be even less than
the code size required for checks. This (wrong) optimization is probably
not worth so just remove it. Removing this also allows igb to assume
aligned accesses for the ethernet header.

Fixes: 3a977deebe ("Intrdocue igb device emulation")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Sriram Yagnaraman <sriram.yagnaraman@est.tech>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit dc9ef1bf454811646b3ee6387f1b96f63f538a18)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>