tcpdump: add SLL parsing support to tcpdump-mini, use -ffunction-sections, -fdata-sections and --gc-sections to reduce size

Backport of r35288

git-svn-id: svn://svn.openwrt.org/openwrt/branches/packages_12.09@35289 3c298f89-4303-0410-b956-a3cf2f4a3e73