cxgbe/t4_tom: Do not uninitialize a toepcb that has not been initialized.

This fixes the following panic:

• trap 0xc, rip = 0xffffffff80c00411, rsp = 0xfffffe0025192840, rbp = 0xfffffe0025192860 ---

vmem_xfree() at vmem_xfree+0xd1/frame 0xfffffe0025192860
tls_uninit_toep() at tls_uninit_toep+0x78/frame 0xfffffe0025192880
free_toepcb() at free_toepcb+0x32/frame 0xfffffe00251928a0
t4_connect() at t4_connect+0x3be/frame 0xfffffe0025192950
tcp_offload_connect() at tcp_offload_connect+0xa4/frame 0xfffffe0025192990
tcp_usr_connect() at tcp_usr_connect+0xec/frame 0xfffffe00251929f0
soconnect() at soconnect+0xae/frame 0xfffffe0025192a30
kern_connectat() at kern_connectat+0xe2/frame 0xfffffe0025192a90
sys_connect() at sys_connect+0x75/frame 0xfffffe0025192ad0
amd64_syscall() at amd64_syscall+0x137/frame 0xfffffe0025192bf0
fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe0025192bf0

• syscall (98, FreeBSD ELF64, sys_connect), rip = 0x8008e9d8a, rsp = 0x7fffffffc0f8, rbp = 0x7fffffffc130 ---

Reviewed by: jhb@
MFC after: 3 days
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D23989