UAVOHoTTBridge: reduced rx/tx-buffers and stack size. fixes a little bug in gps_fix_char.

Saved exactly 1092 bytes of RAM on all targets. Reduced RX and TX
buffers to minimal size and decreased stack size by 100. Added two
missing breaks in gps_fix_char calculation.
Merge pull request #1099 from ernieift/ernieift/HoTT

UAVOHoTTBridge: save 1092 bytes of RAM on all targets.