Adding define for wc_aes_block_size

[night1rider]

Found when compiling with wolfSSL built with --enable-opensslcoexist it will lead to compile errors like:

| ../git/wolfssh/internal.h:462:27: error: 'AES_BLOCK_SIZE' undeclared here (not in a function); did you mean 'WC_AES_BLOCK_SIZE'?
|   462 | #define STATIC_BUFFER_LEN AES_BLOCK_SIZE
|       |                           ^~~~~~~~~~~~~~
| ../git/wolfssh/internal.h:475:31: note: in expansion of macro 'STATIC_BUFFER_LEN'
|   475 |     ALIGN16 byte staticBuffer[STATIC_BUFFER_LEN];

Found this issue when trying to make a yocto image that has wolfSSL, wolfSSH, and wolfProvider. wolfProvider needs opensslcoexist according to documentation.