Make radeapclient build/work in 3.0.x branch

My goal was to have a working version of radeapclient in 3.0.x, *not* to
improve it in any way (for now).
Here is what I did:

1. make the build work.
This includes the following changes:

- undefined references: SSL_*
-> added to .mk: -lssl

- undefined references: radlog_request, radlog_request_error,
rad_assert_fail, radius_exec_program, cf_data_find, cf_section_parse,
cf_data_add, cf_pair_find, cf_pair_value, cf_item_parent,
cf_section_sub_find, cf_sectiontoitem, cf_section_sub_find_name2
-> added to .mk: libfreeradius-server.a

- more undefined references:
pairlist_read, pairlist_free -> main/files.c
rad_fork, rad_waitpid -> main/threads.c

- undefined reference: mainconfig
-> added to radeapclient.c:
struct main_config_t mainconfig;

- problem with "const" qualifiers in FreeRADIUS structures.
Using non "const" pointers to make it build/work.

2. fix the segmentation fault issues.
This includes the following changes:
- after each "paircreate" for an octets or string attribute, allocate a
buffer for vp_strvalue (or vp_octets) through talloc_zero_array (or
talloc_memdup).
- use a talloc'ed eap_packet_t (instead of a static variable) in
functions map_eap_methods and map_eapsim_types (because it is used as a
talloc context by called functions).
- fix the free -> talloc_free issue in eapsimlib.c

3. removed a check that made no sense in sendrecv_eap.

4. tested for EAP/SIM.
NOT tested for EAP/MD5, although I corrected the missing allocation in
the related code.