postfix/tls_policy: Use lmdb map instead of hash

The alpine postfix package seems to have removed support for btree and hash map type. #1918 
The tls_policy.map stuff has been introduced in #1902 and it has been merged without fixing this before (https://github.com/Mailu/Mailu/pull/1902/#issuecomment-902108080)

core/postfix/conf/main.cf

@@ -59,7 +59,7 @@ tls_ssl_options = NO_COMPRESSION, NO_TICKET
 smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
 smtp_tls_protocols =!SSLv2,!SSLv3
 smtp_tls_security_level = {{ OUTBOUND_TLS_LEVEL|default('may') }}
-smtp_tls_policy_maps=hash:/etc/postfix/tls_policy.map
+smtp_tls_policy_maps=lmdb:/etc/postfix/tls_policy.map
 smtp_tls_CApath = /etc/ssl/certs
 smtp_tls_session_cache_database = lmdb:/dev/shm/postfix/smtp_scache
 smtpd_tls_session_cache_database = lmdb:/dev/shm/postfix/smtpd_scache