(legacy) use reverse mask instead of reverse address for ddns in dhcpd (https://github.com/opnsense/core/issues/352)

Crash report would pop up twice, that is confusing.

When changing an existing Phase 1 entry, the value for "Hash algorithm" will always be shown as "MD5" in the edit-screen, although it is configured to something else (i.e. AES).

CRITICAL: When configuring a Phase 2 tunnel and setting P2 protocol to ESP, this setting is ignored. The GUI will show an empty value for P2 protocol and the ipsec.conf will not contain the required "esp" line.

Reported by: @lattera
Reviewed by: @AdSchellevis