dropbear: bump version

Fixes a number of issues. From the changelog:

- Avoid getting stuck in a loop writing huge key files, reported by Bruno
  Thomsen
- Avoid crash on exit due to cleaned up keys before last packets are sent,
  debugged by Ronald Wahl
- Fix a race condition in rekeying where Dropbear would exit if it received a
  still-in-flight packet after initiating rekeying. Reported by Oliver Metz.
  This is a longstanding bug but is triggered more easily since 2013.57
- Ensure that generated RSA keys are always exactly the length
  requested. Previously Dropbear always generated N+16 or N+15 bit keys.
  Thanks to Unit 193
- Fix DROPBEAR_CLI_IMMEDIATE_AUTH mode which saves a network round trip if the
  first public key succeeds. Still not enabled by default, needs more
  compatibility testing with other implementations.
- Fix signal handlers so that errno is saved, thanks to Erik Ahlén for a patch
  and Mark Wickham for independently spotting the same problem.

And at the same time get rid of the TIMEVAL_TO_TIMESPEC as dropbear provides a
fallback implementation if not available (and has done so since 2006).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>