wdogs: Fix counting of free, pre-allocated wdog timers.  The could could get decremented below zero in some situations

recvfrom(): Correct wait for new data when NET_UDP_READAHEAD is enabled.  Fix size accounting when recvfrom_udpreadahead() sets state.rf_recvlen == -1.  I have not checked if data are accumulated to the right position in the buffer however.

Signed-off-by: Pavel Pisa <ppisa@pikron.com>

Added support for other MS58XX altimeters.

Added MS5805 altimeter.