lpm6: fix missing free

lpm6: fix missing free

lpm6 autotests failed with the default alloc of 512M Memory.
While >=2500M was a workaround it became clear while debugging that it
had a leak.
One could see a lot of output like:
  LPM Test tests6[i]: FAIL
  LPM: LPM memory allocation failed

It turned out that in rte_lpm6_free
- lpm might not be freed if it didn't find a te (early return)
- lpm->rules_tbl was not freed ever

Fixes: 899d8bc9b3b5 ("lpm: make tailq fully local")

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>