Asterisk update breaks chan_sip loading

[Marc SCHAEFER <schaefer@alphanet.ch>]

Hello,

the latest asterisk updates, with some documented changes in chan_sip,
has an issue for me (i386):

[Dec  1 08:33:44] WARNING[5039]: loader.c:439 load_dynamic_module: Error loading module 'chan_sip.so': /usr/lib/asterisk/modules/chan_sip.so: undefined symbol: ast_format_cap_count
[Dec  1 08:33:44] WARNING[5039]: loader.c:918 load_resource: Module 'chan_sip.so' could not be loaded.

Version: 1:11.13.1~dfsg-2+deb8u7

In addition, I can't seem to be able to downgrade to the previous release
   apt-get install asterisk=1:11.13.1~dfsg-2+deb8u6 asterisk-config=1:11.13.1~dfsg-2+deb8u6 asterisk-modules=1:11.13.1~dfsg-2+deb8u6 asterisk-voicemail=1:11.13.1~dfsg-2+deb8u6 asterisk-mp3=1:11.13.1~dfsg-2+deb8u6 asterisk-dahdi=1:11.13.1~dfsg-2+deb8u6

as it is no longer in the archive (?).

I could install them manually from my archive backup:
   dpkg -i /backup/backup.0/scratch/mirror/debian/debian-security/pool/updates/main/a/asterisk/asterisk_11.13.1~dfsg-2+deb8u6_i386.deb /backup/backup.0/scratch/mirror/debian/debian-security/pool/updates/main/a/asterisk/asterisk-config_11.13.1~dfsg-2+deb8u6_all.deb /backup/backup.0/scratch/mirror/debian/debian-security/pool/updates/main/a/asterisk/asterisk-dahdi_11.13.1~dfsg-2+deb8u6_i386.deb /backup/backup.0/scratch/mirror/debian/debian-security/pool/updates/main/a/asterisk/asterisk-modules_11.13.1~dfsg-2+deb8u6_i386.deb /backup/backup.0/scratch/mirror/debian/debian-security/pool/updates/main/a/asterisk/asterisk-mp3_11.13.1~dfsg-2+deb8u6_i386.deb /backup/backup.0/scratch/mirror/debian/debian-security/pool/updates/main/a/asterisk/asterisk-voicemail_11.13.1~dfsg-2+deb8u6_i386.deb