seedrng: hoist bb_strtoul out of min/max

- Hoist bb_strtoul out of min/max to prevent quadruple evaluation.
- Don't use separate variables for boottime/realtime.
- Make use of ENABLE_FEATURE_CLEAN_UP where appropriate.
- Order hash initialization after lock taking per Bernhard's taste.
- Add comment description of theory of operation.

function                                             old     new   delta
seed_from_file_if_exists                             533     456     -77
seedrng_main                                        1218    1086    -132
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-209)           Total: -209 bytes
   text	   data	    bss	    dec	    hex	filename
 976445	   4227	   1848	 982520	  efdf8	busybox_old
 976236	   4227	   1848	 982311	  efd27	busybox_unstripped

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
1 file changed