tests: Split dfs_radar into two test cases (dfs_radar1 and dfs_radar2)

tests: Split dfs_radar into two test cases (dfs_radar1 and dfs_radar2)

These DFS radar detection cases were in a single test case to optimize
test execution time with parallel wait for the 60 second CAC. However,
this design has become difficult to support with the kernel changes that
allow radar events to be shared between interfaces. To avoid need for
more workarounds here just for testing purposes, split this into two
test cases so that conflicting events from another interface do not
cause the test case to fail.

Signed-off-by: Jouni Malinen <j@w1.fi>