uthash.h: Add missing default statement in HASH_JEN
uthash.h: Add missing default statement in HASH_JEN

With -Wswitch-default enabled, gcc complains about the missing default in
macro HASH_JEN. The default is not required but included to shut gcc up.

authmillenon/libcoap,authmillenon/libcoap,gebart/libcoap,gebart/libcoap,authmillenon/libcoap,gebart/libcoap