tcpdump: Use -fno-strict-aliasing for now

Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
tcpdump: Remove -O2 hardcode

Use -O2 only if no other optimization level is requested

Change-Id: I18399207ac8d7667a72869fa1039e448aa820d47
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>