mISDNcapid: honour --localstatedir when setting MISDN_CAPI_SOCKET_DIR

[kristovschulz]

Signed-off-by: Christoph Schulz develop@kristov.de

[kkeil]

This pull request is correct an fix a bug in the configure definition, but in the end it also discover a design flaw around the MISDN_CAPI_SOCKET_DIR define. Now the default case (no localstatedir set on the configure run) result in
#define MISDN_CAPI_SOCKET_DIR "${prefix}/run/mISDNcapid"
written in capi20/m_capi_sock.h, which will cause a runtime error later.
I did found no way to get autoconf to substitute "${prefix}" to the real PREFIX in this case.
Maybe to have an own --with-capisocketdir=DIR configure option default to "/run/mISDNcapid" could be a solution or is any auto config guru listening here and know how to get rid of the ${prefix} in this case ?