I have this issue as well, installing mlnx-en-2.3-1.0.0 on CentOS 6.6.
Build output is as follows:
make[1]: Entering directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
CC [M] /tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default/compat/main.o
In file included from /tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default/include/linux/compat-2.6.h:67,
from <command-line>:2:
/tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default/include/linux/compat-2.6.37.h:140: error: redeclaration of enumerator 'ETH_FLAG_TXVLAN'
include/linux/ethtool.h:405: note: previous definition of 'ETH_FLAG_TXVLAN' was here
/tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default/include/linux/compat-2.6.37.h:141: error: redeclaration of enumerator 'ETH_FLAG_RXVLAN'
include/linux/ethtool.h:406: note: previous definition of 'ETH_FLAG_RXVLAN' was here
make[3]: *** [/tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default/compat/main.o] Error 1
make[2]: *** [/tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default/compat] Error 2
make[1]: *** [_module_/tmp/MLNX_EN.11225/BUILD/mlnx-en-2.3/obj/default] Error 2
make[1]: Leaving directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
make: *** [kernel] Error 2
error: Bad exit status from /var/tmp/rpm-tmp.Nq8AHn (%build)
Are there patches or driver updates for RHEL/CentOS 6.6?