batman-adv: return proper value in case of hash_add failure
batman-adv: return proper value in case of hash_add failure

In case of hash_add failure tt_global_add() must return 0 (which means on entry
insertion).

Signed-off-by: Antonio Quartulli <ed91ce0fd2670d4a98b12fc9ec6b7a497c7ed53f@autistici.org>

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