MINOR: ocsp: put internal functions as static ones

MINOR: ocsp: put internal functions as static ones

-Wmissing-prototypes let us check which functions can be made static and
is not used elsewhere.

rc/ssl_ocsp.c:1079:5: error: no previous prototype for ‘ssl_ocsp_update_insert_after_error’ [-Werror=missing-prototypes]
 1079 | int ssl_ocsp_update_insert_after_error(struct certificate_ocsp *ocsp)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/ssl_ocsp.c:1116:6: error: no previous prototype for ‘ocsp_update_response_stline_cb’ [-Werror=missing-prototypes]
 1116 | void ocsp_update_response_stline_cb(struct httpclient *hc)
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/ssl_ocsp.c:1127:6: error: no previous prototype for ‘ocsp_update_response_headers_cb’ [-Werror=missing-prototypes]
 1127 | void ocsp_update_response_headers_cb(struct httpclient *hc)
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/ssl_ocsp.c:1138:6: error: no previous prototype for ‘ocsp_update_response_body_cb’ [-Werror=missing-prototypes]
 1138 | void ocsp_update_response_body_cb(struct httpclient *hc)
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/ssl_ocsp.c:1149:6: error: no previous prototype for ‘ocsp_update_response_end_cb’ [-Werror=missing-prototypes]
 1149 | void ocsp_update_response_end_cb(struct httpclient *hc)
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~
src/ssl_ocsp.c:2095:5: error: no previous prototype for ‘ocsp_update_postparser_init’ [-Werror=missing-prototypes]
 2095 | int ocsp_update_postparser_init()
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~