configure.ac: Require libosmocore 1.2.0

Current code uses GSM23003_MSISDN_MAX_DIGITS, which is only available in
libosmocore 1.2.0 onwards. Let's update configure.ac accordingly.

Fixes: 2e403d6c3f0caa4fd40e8cab8acd6586deadfdf8
Change-Id: Iad03a8cf7a36bdc824ec2acc8fb8f9c27a1c0421
1 file changed