netmap-modules: fix compilation failure

If CONFIG_IXGBE is enabled in kernel. This package fails to build with
error messages like below.

|  #error "unsupported ixgbe driver version"
|   ^

.......

error: request for member 'count' in something not a structure or union
|   na.num_rx_desc = NM_IXGBE_RX_RING(adapter, 0)->count;
|                                                ^
| cc1: some warnings being treated as errors

Fix this problem by disabling igxbe driver in netmap-modules.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>