security/pks: the port had been further improved (+)

- Simplify Berkeley DB detection (rather than completely deleting
  the corresponding configure script section, assume that if user
  passes DBHDR she knows what she's doing and trust that value)
- Fix a harmless typo RSA_get0_p() -> DSA_get0_p() in the previous
  commit 6074b736
- GC some more needless variables (MAKE_ENV, LDFLAGS) and enable
  IPv6 while I'm here