Bump SONAME of libzfs and libzpool

The ABI of libzfs and libzpool have breaking changes since the
last major release. Bump the SONAME for the upcoming 2.4 release
branch to libzfs7 and libzpool7.

Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #17911