bearssl: remove incorrect const on variable that is modified #7133
A recent vtls cleanup accidentally made a variable const that was modified later on in the function, causing a build failure when BearSSL is enabled. To prevent this sort of thing in the future, I added BearSSL to the Travis configuration.
While testing the Travis build, I noticed a warning that it was missing explicit initializers for a couple
hostname may be set to NULL later on in this function if it is an IP address.
Also, add comments like the other vtls backends.
Also, add comments like the other vtls backends. Closes #7133