hash: fix icc build

hash: fix icc build

build error with icc version 17.0.4 (gcc version 7.0.0 compatibility):

In file included from .../dpdk/lib/librte_hash/rte_fbk_hash.h(59),
                 from .../dpdk/lib/librte_hash/rte_fbk_hash.c(54):
.../dpdk/x86_64-native-linuxapp-icc/include/rte_hash_crc.h(480):
 error #1292: unknown attribute "fallthrough"
                __attribute__ ((fallthrough));
                                ^

In file included from .../dpdk/lib/librte_hash/rte_fbk_hash.h(59),
                 from .../dpdk/lib/librte_hash/rte_fbk_hash.c(54):
.../dpdk/x86_64-native-linuxapp-icc/include/rte_hash_crc.h(486):
 error #1292: unknown attribute "fallthrough"
                __attribute__ ((fallthrough));
                                ^
This code patch hit when gcc > 7 installed and ICC doesn't recognize
fallthrough attribute.

Fixed by disabling code when compiled with ICC.

Fixes: 3dfb9facb055 ("lib: add switch fall-through comments")

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>