tests: Improve test suite for peer attributes

tests: Improve test suite for peer attributes

This commit improves the previous implementation of the peer attribute
test suite by getting rid of some really ugly macros and replacing them
with sane functions.

Additionally, the macro TEST_ASSERT was changed to TEST_ASSERT_EQ (==
comparison) which now also prints the line where the assertion has been
infringend. This should make it way more clear where a specific issue
has been spotted.

Last but not least, the multicast families for both IPv4 and IPv6 had
been added as they are working without any further changes or special
cases for all currently existing peer attributes. Other AFI/SAFI
references have been removed to keep the code clean.

Signed-off-by: Pascal Mathis <mail@pascalmathis.com>