Revert "mavlink: revert stack size 2048 to fix suspending in HIL mode"

This reverts commit eb177def141d321b43a4c20819179423e128a92f.
Revert "Merge pull request #620 from pigeonhunter/stack_sizes"

This reverts commit 3b31a6b1b9756eb191eaaafb1c137e6874079281, reversing
changes made to 70afb3ca3b3f1844241c9c9312579bbb2475232c.