smtp: sync in-code defaults with configuration file - v1

[jasonish]

Currently the default suricata.yaml sets some values that do not
reflect the default values in the code. As most users are probably
using a default suricata.yaml, make the code have the same defaults as
in suricata.yaml:

• mime.decode-mime: false -> true
• mime.decode-base64: false -> true
• mime.decode-quoted-printable: false -> true
• mime.extract-urls: false -> true

I guess the question is if its OK for a simple configuration of:

app-layer:
  protocols:
    smtp:
      enabled: yes

to acquire these new defaults.

Ticket: https://redmine.openinfosecfoundation.org/issues/5823

[suricata-qa]

WARNING:

field	baseline	test	%
	SURI_TLPW1_stats_chk
.flow.end.tcp_state.last_ack	1004	257	25.6%
	SURI_TLPR1_stats_chk
.flow.end.tcp_state.fin_wait2	156072	127814	81.89%

Pipeline 12751

[victorjulien]

Merged in #8605, thanks!