[IPV4] IP_GRE: Unify code path to get hash array index.
[IPV4] IP_GRE: Unify code path to get hash array index.

Signed-off-by: YOSHIFUJI Hideaki <948b80da4254122ea1e8973dd9930d46b7654cf3@linux-ipv6.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs