There were different tags defined in testcase.ini files for
networking tests. Unify these and change the tag to "net"
in all networking tests. This makes it easy to execute
all network tests via sanitycheck.
Change-Id: I8ce7ccf8cccca35234602e37f6568db0b986d181
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>