sip/auth: add algorithm=MD5

[sreimers]

Fixes #85

[codecov]

Codecov Report

Merging #86 (08755e5) into master (00fdc24) will increase coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head 08755e5 differs from pull request most recent head d2c1002. Consider uploading reports for the commit d2c1002 to get more accurate results

@@            Coverage Diff             @@
##           master      #86      +/-   ##
==========================================
+ Coverage   53.30%   53.32%   +0.01%     
==========================================
  Files         192      192              
  Lines       21473    21475       +2     
==========================================
+ Hits        11447    11452       +5     
+ Misses      10026    10023       -3     

Impacted Files	Coverage Δ
src/sip/auth.c	12.30% <0.00%> (-0.10%)	⬇️
src/list/list.c	85.29% <0.00%> (-0.74%)	⬇️
src/mbuf/mbuf.c	79.06% <0.00%> (+0.12%)	⬆️
src/sip/transp.c	37.39% <0.00%> (+0.43%)	⬆️
src/json/decode.c	94.71% <0.00%> (+0.81%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 00fdc24...d2c1002. Read the comment docs.