Fix doxygen warnings

[alfredh]

Fixes the warnings:

alfredh@debian:~/git/re$ doxygen mk/Doxyfile 
/home/alfredh/git/re/src/mod/mod_internal.h:15: warning: argument 'h' from the argument list of _mod_close has multiple @param documentation sections
/home/alfredh/git/re/src/mod/mod_internal.h:13: warning: argument 'name' from the argument list of _mod_open has multiple @param documentation sections
/home/alfredh/git/re/src/mod/mod_internal.h:14: warning: argument 'h' from the argument list of _mod_sym has multiple @param documentation sections
/home/alfredh/git/re/src/mod/mod_internal.h:14: warning: argument 'symbol' from the argument list of _mod_sym has multiple @param documentation sections
/home/alfredh/git/re/include/re_net.h:73: warning: argument 'ifh' from the argument list of net_if_list has multiple @param documentation sections
/home/alfredh/git/re/include/re_net.h:73: warning: argument 'arg' from the argument list of net_if_list has multiple @param documentation sections
/home/alfredh/git/re/src/tls/openssl/tls.c:1940: warning: argument 'hc' of command @param is not found in the argument list of STACK_OF(X509 *)
/home/alfredh/git/re/src/tls/openssl/tls.c:1940: warning: argument 'hc' of command @param is not found in the argument list of STACK_OF(X509 *)