netdev-linux: Remove unreachable code in netdev_linux_rx_recv_tap().

netdev-linux: Remove unreachable code in netdev_linux_rx_recv_tap().

While splitting netdev_linux_rx_recv() into netdev_linux_rx_recv_sock()
and netdev_linux_rx_recv_tap() in commit
b73c85181df9 ("netdev-linux: Read packet auxdata to obtain vlan_tid")
error handling part was copied 'as is' to both functions.
But in case of netdev_linux_rx_recv_tap(), according to POSIX, the
number of bytes read shall never be greater than 'size'.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>