baresip: forked INVITE causes PRACKs to be sent with equal tags

Scenario:

• UAC jh@test.tutpro.com sends INVITE to test@test.tutpro.com
• sip proxy forks the INVITE to two registered UASes
• both UASes response with 180 ringing
• UAC sends PRACK to both and both PRACKs have equal tags

Issue: second PRACK should have had To tag from the second 180 response, i.e. 149eb80cb71e5a38.

17:11:18.082#
TCP 192.168.238.45:56852 -> 192.168.238.215:5060
INVITE sip:test@test.tutpro.com SIP/2.0
Via: SIP/2.0/TCP 192.168.238.45:46149;branch=z9hG4bKb4f897122cc2f136;rport
Contact: <sip:jh@test.tutpro.com;gr=urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce>
Max-Forwards: 70
Route: <sip:siika.tutpro.com:5060;transport=tcp;lr>
To: <sip:test@test.tutpro.com>
From: "Juha" <sip:jh@test.tutpro.com>;tag=3f1a28c9ee7a4304
Call-ID: a30edcfbf0b7559c
CSeq: 51283 INVITE
User-Agent: baresip v2.7.0 (x86_64/linux)
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,NOTIFY,SUBSCRIBE,INFO,MESSAGE,UPDATE,PRACK,REFER
Supported: gruu,path,outbound,replaces,100rel
Content-Type: application/sdp
Content-Length: 415

...

17:11:18.162#
TCP 192.168.238.215:5060 -> 192.168.238.45:56852
SIP/2.0 180 Ringing
Record-Route: <sip:192.168.238.215;transport=tcp;lr>
Via: SIP/2.0/TCP 192.168.238.45:46149;received=192.168.238.45;branch=z9hG4bKb4f897122cc2f136;rport=56852
To: <sip:test@test.tutpro.com>;tag=331068bf5177905c
From: "Juha" <sip:jh@test.tutpro.com>;tag=3f1a28c9ee7a4304
Call-ID: a30edcfbf0b7559c
CSeq: 51283 INVITE
Server: baresip v2.7.0 (x86_64/linux)
Contact: <sip:test@test.tutpro.com;gr=urn:uuid:59f2124b-bbf0-06b4-0316-c750c420cdb3>
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,NOTIFY,SUBSCRIBE,INFO,MESSAGE,UPDATE,PRACK,REFER
Require: 100rel
RSeq: 22797
Content-Length: 0

call: SIP Progress: 180 Ringing (/)
alsa: reset: srate=8000, ch=1, num_frames=320, pcmfmt=S16_LE
alsa: playback started (default)

17:11:18.255#
TCP 192.168.238.45:56852 -> 192.168.238.215:5060
PRACK sip:test@test.tutpro.com;gr=urn:uuid:59f2124b-bbf0-06b4-0316-c750c420cdb3 SIP/2.0
Via: SIP/2.0/TCP 192.168.238.45:46149;branch=z9hG4bK760fa11d887974b5;rport
Max-Forwards: 70
Route: <sip:192.168.238.215;transport=tcp;lr>
To: <sip:test@test.tutpro.com>;tag=331068bf5177905c
From: "Juha" <sip:jh@test.tutpro.com>;tag=3f1a28c9ee7a4304
Call-ID: a30edcfbf0b7559c
CSeq: 51284 PRACK
User-Agent: baresip v2.7.0 (x86_64/linux)
RAck: 22797 51283 INVITE
Content-Length: 0


17:11:18.255#
TCP 192.168.238.215:5060 -> 192.168.238.45:56852
SIP/2.0 180 Ringing
Record-Route: <sip:192.168.238.215;transport=tcp;lr>
Via: SIP/2.0/TCP 192.168.238.45:46149;received=192.168.238.45;branch=z9hG4bKb4f897122cc2f136;rport=56852
To: <sip:test@test.tutpro.com>;tag=149eb80cb71e5a38
From: "Juha" <sip:jh@test.tutpro.com>;tag=3f1a28c9ee7a4304
Call-ID: a30edcfbf0b7559c
CSeq: 51283 INVITE
Server: baresip v2.7.0 (x86_64/linux)
Contact: <sip:test@test.tutpro.com;gr=urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce>
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,NOTIFY,SUBSCRIBE,INFO,MESSAGE,UPDATE,PRACK,REFER
Require: 100rel
RSeq: 26825
Content-Length: 0

call: SIP Progress: 180 Ringing (/)

17:11:18.255#
TCP 192.168.238.45:56852 -> 192.168.238.215:5060
PRACK sip:test@test.tutpro.com;gr=urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce SIP/2.0
Via: SIP/2.0/TCP 192.168.238.45:46149;branch=z9hG4bKff951fb4505a52e9;rport
Max-Forwards: 70
Route: <sip:192.168.238.215;transport=tcp;lr>
To: <sip:test@test.tutpro.com>;tag=331068bf5177905c
From: "Juha" <sip:jh@test.tutpro.com>;tag=3f1a28c9ee7a4304
Call-ID: a30edcfbf0b7559c
CSeq: 51285 PRACK
User-Agent: baresip v2.7.0 (x86_64/linux)
RAck: 26825 51283 INVITE
Content-Length: 0