wireshark: update to latest stable version

Version 1.12.0 is out, update the SRC_URI and associated variables.

Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>
README: Update layer dependencies

There are a few recipes in meta-networking that depend unconditionally on
components in meta-oe, so indicate that in the README.

Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>
wireshark: update README instructions

Minor tweaks to the README to make the email suggestion follow the format
used in other meta-openembedded README files and adding clarification on
building wireshark in a GUI environment.

Acked-by: Armin Kuster <akuster@mvista.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>